Integration of pathological criteria and immunohistochemical evaluation for invasive lobular carcinoma diagnosis: recommendations from the European Lobular Breast Cancer Consortium

Invasive lobular carcinoma (ILC) is the second most frequent type of breast cancer (BC) and its peculiar morphology is mainly driven by inactivation of CDH1, the gene coding for E-cadherin cell adhesion protein. ILC-specific therapeutic and disease-monitoring approaches are gaining momentum in the clinic, increasing the importance of accurate ILC diagnosis. Several essential and desirable morphological diagnostic criteria are currently defined by the World Health Organization, the routine use of immunohistochemistry (IHC) for E-cadherin is not recommended. Disagreement in the diagnosis of ILC has been repeatedly reported, but inter-pathologist agreement increases with the use of E-cadherin IHC. In this study, we aimed to harmonize the pathological diagnosis of ILC by comparing five commonly used E-cadherin antibody clones (NCH-38, EP700Y, Clone 36, NCL-L-E-cad [Clone 36B5], and ECH-6). We determined their biochemical specificity for the E-cadherin protein and IHC staining performance according to type and location of mutation on the CDH1 gene. Western blot analysis on mouse cell lines with conditional E-cadherin expression revealed a reduced specificity of EP700Y and NCL-L-E-cad for E-cadherin, with cross-reactivity of Clone 36 to P-cadherin. The use of IHC improved inter-pathologist agreement both for ILC as well as for lobular carcinoma in situ and atypical lobular hyperplasia. The E-cadherin IHC staining pattern was associated with variant allele frequency and likelihood of non-sense mediated RNA decay but not with the type or position of CDH1 mutations. Based on these results, we make recommendations for the indication for E-cadherin staining, choice of antibodies, and their interpretation in order to standardize ILC diagnosis in current pathology practice.

Metastases of primary mixed no-special type and lobular breast cancer display an exclusive lobular histology

Primary tumors with a mixed invasive breast carcinoma of no-special type (IBC-NST) and invasive lobular cancer (ILC) histology are present in approximately five percent of all patients with breast cancer and are understudied at the metastatic level. Here, we characterized the histology of metastases from two patients with primary mixed IBC-NST/ILC from the postmortem tissue donation program UPTIDER (NCT04531696). The 14 and 43 metastatic lesions collected at autopsy had morphological features and E-cadherin staining patterns consistent with pure ILC. While our findings still require further validation, they may challenge current clinical practice and imaging modalities used in these patients.

Serum methylmalonic acid concentrations at breast cancer diagnosis significantly correlate with clinical frailty

Methylmalonic acid (MMA), a by-product of propionate metabolism, is known to increase with age. This study investigates the potential of serum MMA concentrations as a biomarker for age-related clinical frailty in older patients with breast cancer. One hundred nineteen patients ≥ 70 years old with early-stage breast cancer were included (median age 76 years). G8 screening, full geriatric assessment, clinical parameters (i.e., estimated glomerular filtration rate (eGFR) and body mass index (BMI)), and serum sample collection were collected at breast cancer diagnosis before any therapy was administered. MMA concentrations were measured via liquid chromatography with tandem mass spectrometry. MMA concentrations significantly increased with age and eGFR (all P < 0.001) in this older population. The group with an abnormal G8 (≤ 14, 51% of patients) had significantly higher MMA levels than the group with normal G8 (> 14, 49%): 260 nmol/L vs. 188 nmol/L, respectively (P = 0.0004), even after correcting for age and eGFR (P = 0.001). Furthermore, in the detailed assessment, MMA concentrations correlated most with mobility (Eastern Cooperative Oncology Group (ECOG) Performance Status and Activities of Daily Living (ADL) tools, all P ≤ 0.02), comorbidity (Charlson Comorbidity Index (CCI) tool, P = 0.005), and polypharmacy (P < 0.001), whereas no significant associations were noted for instrumental ADL (IADL), Mini-Mental State Examination (MMSE), Geriatric Depression Scale-15 (GDS15), Mini Nutritional Assessment-Short Form (MNA-SF), and pain (all P > 0.1). In addition, our results showed that higher MMA levels correlate with poor overall survival in breast cancer patients (P = 0.003). Elevated serum MMA concentrations at initial diagnosis are significantly associated, not only with age but also independently with clinical frailty, suggesting a possible influence of MMA on clinical frailty in older patients with early-stage breast cancer.

Reporting on invasive lobular breast cancer in clinical trials: a systematic review

Invasive lobular breast cancer (ILC) differs from invasive breast cancer of no special type in many ways. Evidence on treatment efficacy for ILC is, however, lacking. We studied the degree of documentation and representation of ILC in phase III/IV clinical trials for novel breast cancer treatments. Trials were identified on Pubmed and clinicaltrials.gov. Inclusion/exclusion criteria were reviewed for requirements on histological subtype and tumor measurability. Documentation of ILC was assessed and ILC inclusion rate, central pathology and subgroup analyses were evaluated. Inclusion restrictions concerning tumor measurability were found in 39/93 manuscripts. Inclusion rates for ILC were documented in 13/93 manuscripts and varied between 2.0 and 26.0%. No central pathology for ILC was reported and 3/13 manuscripts had ILC sub-analyses. ILC is largely disregarded in most trials with poor representation and documentation. The current inclusion criteria using RECIST v1.1, fall short in recognizing the unique non-measurable metastatic infiltration of ILC.

Aging-accumulated methylmalonic acid serum levels at breast cancer diagnosis are not associated with distant metastases

PURPOSE

Recent evidence suggests that age-accumulated methylmalonic acid (MMA) promotes breast cancer progression in mice. This study aims to investigate the association between baseline serum MMA concentrations in patients with breast cancer and the development of subsequent distant metastases.

METHODS

We included 32 patients with early Luminal B-like breast cancer (LumB, median age 62.4y) and 52 patients with early triple-negative breast cancer (TNBC, median age 50.5y) who developed distant metastases within 5 years. They were matched to an equal number of early breast cancer patients (median age 62.2y for LumB and 50.5y for TNBC) who did not develop distant metastases with at least 5 years of follow-up.

RESULTS

Baseline serum MMA levels at breast cancer diagnosis showed a positive correlation with age (P < 0.001) and a negative correlation with renal function and vitamin B12 (all P < 0.02), but no statistical association was found with BMI or tumor stage (P > 0.6). Between matched pairs, no significant difference was observed in MMA levels, after adjusting for kidney function and age (P = 0.19). Additionally, in a mouse model, a significant decline in MMA levels was observed in the tumor-bearing group compared to the group without tumors before and after tumor establishment or at identical times for the control group (P = 0.03).

CONCLUSION

Baseline serum MMA levels in patients with breast cancer are not correlated with secondary distant metastasis. Evidence in the mouse model suggests that the presence of a tumor perturbates MMA levels.

Treatment Response, Tumor Infiltrating Lymphocytes and Clinical Outcomes in Inflammatory Breast Cancer-Treated with Neoadjuvant Systemic Therapy

Inflammatory breast cancer (IBC) is a rare (1%-5%), aggressive form of breast cancer, accounting for approximately 10% of breast cancer mortality. In the localized setting, standard of care is neoadjuvant chemotherapy (NACT) ± anti-HER2 therapy, followed by surgery. Here we investigated associations between clinicopathologic variables, stromal tumor-infiltrating lymphocytes (sTIL), and pathologic complete response (pCR), and the prognostic value of pCR. We included 494 localized patients with IBC treated with NACT from October 1996 to October 2021 in eight European hospitals. Standard clinicopathologic variables were collected and central pathologic review was performed, including sTIL. Associations were assessed using Firth logistic regression models. Cox regressions were used to evaluate the role of pCR and residual cancer burden (RCB) on disease-free survival (DFS), distant recurrence-free survival (DRFS), and overall survival (OS). Distribution according to receptor status was as follows: 26.4% estrogen receptor negative (ER-)/HER2-; 22.0% ER-/HER2+; 37.4% ER+/HER2-, and 14.1% ER+/HER2+. Overall pCR rate was 26.3%, being highest in the HER2+ groups (45.9% for ER-/HER2+ and 42.9% for ER+/HER2+). sTILs were low (median: 5.3%), being highest in the ER-/HER2- group (median: 10%). High tumor grade, ER negativity, HER2 positivity, higher sTILs, and taxane-based NACT were significantly associated with pCR. pCR was associated with improved DFS, DRFS, and OS in multivariable analyses. RCB score in patients not achieving pCR was independently associated with survival. In conclusion, sTILs were low in IBC, but were predictive of pCR. Both pCR and RCB have an independent prognostic role in IBC treated with NACT.

SIGNIFICANCE

IBC is a rare, but very aggressive type of breast cancer. The prognostic role of pCR after systemic therapy and the predictive value of sTILs for pCR are well established in the general breast cancer population; however, only limited information is available in IBC. We assembled the largest retrospective IBC series so far and demonstrated that sTIL is predictive of pCR. We emphasize that reaching pCR remains of utmost importance in IBC.

Histopathological growth patterns and tumor-infiltrating lymphocytes in breast cancer liver metastases

Liver is the third most common organ for breast cancer (BC) metastasis. Two main histopathological growth patterns (HGP) exist in liver metastases (LM): desmoplastic and replacement. Although a reduced immunotherapy efficacy is reported in patients with LM, tumor-infiltrating lymphocytes (TIL) have not yet been investigated in BCLM. Here, we evaluate the distribution of the HGP and TIL in BCLM, and their association with clinicopathological variables and survival. We collect samples from surgically resected BCLM (n = 133 patients, 568 H&E sections) and post-mortem derived BCLM (n = 23 patients, 97 H&E sections). HGP is assessed as the proportion of tumor liver interface and categorized as pure-replacement ('pure r-HGP') or any-desmoplastic ('any d-HGP'). We score the TIL according to LM-specific guidelines. Associations with progression-free (PFS) and overall survival (OS) are assessed using Cox regressions. We observe a higher prevalence of 'any d-HGP' (56%) in the surgical samples and a higher prevalence of 'pure r-HGP' (83%) in the post-mortem samples. In the surgical cohort, no evidence of the association between HGP and clinicopathological characteristics is observed except with the laterality of the primary tumor (p value = 0.049) and the systemic preoperative treatment before liver surgery (p value = .039). TIL is less prevalent in 'pure r-HGP' as compared to 'any d-HGP' (p value = 0.001). 'Pure r-HGP' predicts worse PFS (HR: 2.65; CI: (1.45-4.82); p value = 0.001) and OS (HR: 3.10; CI: (1.29-7.46); p value = 0.011) in the multivariable analyses. To conclude, we demonstrate that BCLM with a 'pure r-HGP' is associated with less TIL and with the worse outcome when compared with BCLM with 'any d-HGP'. These findings suggest that HGP could be considered to refine treatment approaches.

High-grade HER2-positive mucoepidermoid carcinoma of the breast: a case report and review of the literature

BACKGROUND

Mucoepidermoid carcinoma of the breast is a rare special type of salivary gland-like tumor of the breast, usually displaying triple-negative phenotype. To date, only 64 cases have been reported in the English literature. Herein, we report the first case of mucoepidermoid carcinoma of the breast with human epidermal growth factor receptor 2 gene amplification.

CASE PRESENTATION

A 58-year-old Caucasian woman treated with breast-conserving surgery, radiotherapy, and chemotherapy for an invasive breast carcinoma of no special type, relapsed 20 years later in the ipsilateral left breast. Histological examination of the core needle biopsy of the relapse deferred to the surgical specimen for the definitive diagnosis, because of the broad differential diagnosis. On the resected specimen we observed the presence of a poorly differentiated carcinoma with mucoepidermoid carcinoma of the breast typical features consisting of epidermoid, intermediate and mucinous cells lacking true keratinization, in keeping with the latest World Health Organization diagnostic criteria. The mucoepidermoid carcinoma of the breast was weakly estrogen receptor and androgen receptor positive and progesterone receptor negative, but exceptionally showed human epidermal growth factor receptor 2 gene amplification. Mastermind-like transcriptional coactivator 2 gene translocations were not detected by fluorescent in situ hybridization. The patient received adjuvant chemotherapy with anti-human epidermal growth factor receptor 2 therapy but no endocrine therapy. After 61 months of follow-up, no signs of local or distant recurrence were observed.

CONCLUSIONS

Mucoepidermoid carcinoma of the breast is a very rare entity. Despite being most frequently triple negative, the standard evaluation of receptor status is mandatory, as well as strict application of World Health Organization diagnostic criteria for correct patient management.

Circulating biomarkers at diagnosis correlate with distant metastases of early luminal-like breast cancer

There is an urgent need for new and better biomarker modalities to estimate the risk of recurrence within the luminal-like breast cancer (BC) population. Molecular diagnostic tests used in the clinic lack accuracy in identifying patients with early luminal BC who are likely to develop metastases. This study provides proof of concept that various liquid biopsy read-outs could serve as valuable candidates to build a multi-modal biomarker model distinguishing, already at diagnosis, between early metastasizing and non-metastasizing patients. All these blood biomarkers (chemokines, microRNAs, leukemia inhibitory factor, osteopontin, and serum-induced functional myeloid signaling responses) can be measured in baseline plasma/serum samples and could be added to the existing prognostic factors to improve risk stratification and more patient-tailored treatment in early luminal BC.

Poor Outcome in Postpartum Breast Cancer Patients Is Associated with Distinct Molecular and Immunologic Features

PURPOSE

Patients with postpartum breast cancer diagnosed after cessation of breastfeeding (postweaning, PP-BCPW) have a particularly poor prognosis compared with patients diagnosed during lactation (PP-BCDL), or to pregnant (Pr-BC) and nulliparous (NP-BC) patients, regardless of standard prognostic characteristics. Animal studies point to a role of the involution process in stimulation of tumor growth in the mammary gland. However, in women, the molecular mechanisms that underlie this poor prognosis of patients with PP-BCPW remain vastly underexplored, due to of lack of adequate patient numbers and outcome data.

EXPERIMENTAL DESIGN

We explored whether distinct prognostic features, common to all breast cancer molecular subtypes, exist in postpartum tumor tissue. Using detailed breastfeeding data, we delineated the postweaning period in PP-BC as a surrogate for mammary gland involution and performed whole transcriptome sequencing, immunohistochemical, and (multiplex) immunofluorescent analyses on tumor tissue of patients with PP-BCPW, PP-BCDL, Pr-BC, and NP-BC.

RESULTS

We found that patients with PP-BCPW having a low expression level of an immunoglobulin gene signature, but high infiltration of plasma B cells, have an increased risk for metastasis and death. Although PP-BCPW tumor tissue was also characterized by an increase in CD8+ cytotoxic T cells and reduced distance among these cell types, these parameters were not associated with differential clinical outcomes among groups.

CONCLUSIONS

These data point to the importance of plasma B cells in the postweaning mammary tumor microenvironment regarding the poor prognosis of PP-BCPW patients. Future prospective and in-depth research needs to further explore the role of B-cell immunobiology in this specific group of young patients with breast cancer.

Association of body mass index with clinicopathological features and survival in patients with primary invasive lobular breast cancer

PURPOSE

Invasive lobular carcinoma (ILC) represents up to 15% of all breast carcinomas. While the proportion of women with overweight and obesity increases globally, the impact of body mass index (BMI) at primary diagnosis on clinicopathological features of ILC and the prognosis of the patients has not been investigated yet.

PATIENTS AND METHODS

We performed a multicentric retrospective study including patients diagnosed with non-metastatic pure ILC. The association of BMI at diagnosis with clinicopathological variables was assessed using linear or multinomial logistic regression. Univariable and multivariable survival analyses were performed to evaluate the association of BMI with disease-free survival (DFS), distant recurrence-free survival (DRFS), and overall survival (OS).

RESULTS

The data of 2856 patients with ILC and available BMI at diagnosis were collected, of which 2570/2856 (90.0%) had oestrogen receptor (ER)-positive and human epidermal growth factor receptor (HER2) not amplified/overexpressed (ER+/HER2-) ILC. Of these 2570 patients, 80 were underweight (3.1%), 1410 were lean (54.9%), 712 were overweight (27.7%), and 368 were obese (14.3%). Older age at diagnosis, a higher tumour grade, a larger tumour size, a nodal involvement, and multifocality were associated with a higher BMI. In univariable models, higher BMI was associated with worse outcomes for all end-points (DFS: hazard ratio (HR) 1.21, 95CI 1.12-1.31, p value<0.01; DRFS: HR 1.25, 95CI 1.12-1.40, p value<0.01; OS: HR 1.25, 95CI 1.13-1.37, p value<0.01). This association was not statistically significant in multivariable analyses (DFS: HR 1.09, 95CI 0.99-1.20, p value 0.08; DRFS: HR 1.03, 95CI 0.89-1.20, p value 0.67; OS: HR 1.11, 95CI 0.99-1.24, p value 0.08), whereas grade, tumour size, and nodal involvement were still prognostic for all end-points.

CONCLUSION

Worse prognostic factors such as higher grade, larger tumour size, and nodal involvement are associated with higher BMI in ER+/HER2- ILC, while there was no statistical evidence for an independent prognostic role for BMI. Therefore, we hypothesise that the effect of BMI on survival could be mediated through its association with these clinicopathological variables.

Differences in the Tumor Molecular and Microenvironmental Landscape between Early (Non-Metastatic) and De Novo Metastatic Primary Luminal Breast Tumors

Background: The molecular mechanisms underlying the de novo metastasis of luminal breast cancer (dnMBC) remain largely unknown. Materials and Methods: Newly diagnosed dnMBC patients (grade 2/3, ER+, PR+/-, HER2-), with available core needle biopsy (CNB), collected from the primary tumor, were selected from our clinical-pathological database. Tumors from dnMBC patients were 1:1 pairwise matched (n = 32) to tumors from newly diagnosed patients who had no distant metastases at baseline (eBC group). RNA was extracted from 5 × 10 µm sections of FFPE CNBs. RNA sequencing was performed using the Illumina platform. Differentially expressed genes (DEG)s were assessed using EdgeR; deconvolution was performed using CIBERSORTx to assess immune cell fractions. A paired Wilcoxon test was used to compare dnMBC and eBC groups and corrected for the false discovery rate. Results: Many regulatory DEGs were significantly downregulated in dnMBC compared to eBC. Also, immune-related and hypoxia-related signatures were significantly upregulated. Paired Wilcoxon analysis showed that the CCL17 and neutrophils fraction were significantly upregulated, whereas the memory B-cell fraction was significantly downregulated in the dnMBC group. Conclusions: Primary luminal tumors of dnMBC patients display significant transcriptomic and immunological differences compared to comparable tumors from eBC patients.

Obesity-associated changes in molecular biology of primary breast cancer

Obesity is associated with an increased risk of developing breast cancer (BC) and worse prognosis in BC patients, yet its impact on BC biology remains understudied in humans. This study investigates how the biology of untreated primary BC differs according to patients' body mass index (BMI) using data from >2,000 patients. We identify several genomic alterations that are differentially prevalent in overweight or obese patients compared to lean patients. We report evidence supporting an ageing accelerating effect of obesity at the genetic level. We show that BMI-associated differences in bulk transcriptomic profile are subtle, while single cell profiling allows detection of more pronounced changes in different cell compartments. These analyses further reveal an elevated and unresolved inflammation of the BC tumor microenvironment associated with obesity, with distinct characteristics contingent on the estrogen receptor status. Collectively, our analyses imply that obesity is associated with an inflammaging-like phenotype. We conclude that patient adiposity may play a significant role in the heterogeneity of BC and should be considered for BC treatment tailoring.

Intra-patient and inter-metastasis heterogeneity of HER2-low status in metastatic breast cancer

INTRODUCTION

Anti-HER2 antibody-drug conjugates (ADCs) have shown important efficacy in HER2-low metastatic breast cancer (mBC). Criteria for receiving ADCs are based on a single assay on the primary tumour or a small metastatic biopsy. We assessed the intra-patient inter-metastasis heterogeneity of HER2-low status in HER2-negative mBC.

PATIENTS AND METHODS

We included samples of 10 patients (7 ER-positive and 3 ER-negative) donated in the context of our post-mortem tissue donation program UPTIDER. Excisional post-mortem biopsies of 257 metastases and 8 breast tumours underwent central HER2 immunohistochemistry (IHC), alongside 41 pre-mortem primary or metastatic samples. They were classified as HER2-zero, HER2-low (HER2-1+ or HER2-2+, in situ hybridisation [ISH] negative) or HER2-positive (HER2-3+ or HER2-2+, ISH-positive) following ASCO/CAP guidelines 2018. HER2-zero was further subdivided into HER2-undetected (no staining) and HER2-ultralow (faint staining in ≤10% of tumour cells).

RESULTS

Median post-mortem interval was 2.5 h. In 8/10 patients, HER2-low and HER2-zero metastases co-existed, with the proportion of HER2-low lesions ranging from 5% to 89%. A total of 32% of metastases currently classified as HER2-zero were HER2-ultralow. Intra-organ inter-metastasis heterogeneity of HER2-scores was observed in the liver in 3/6 patients. Patients with primary ER-positive disease had a higher proportion of HER2-low metastases as compared to ER-negative disease (46% versus 8%, respectively). At the metastasis level, higher percentages of ER-expressing cells were observed in HER2-low or -ultralow as compared to HER2-undetected metastases.

CONCLUSIONS

Important intra-patient inter-metastasis heterogeneity of HER2-low status exists. This questions the validity of HER2-low in its current form as a theranostic marker.

Abstract 6773: Spatial dynamics of cytotoxic T lymphocyte exhaustion in reactive and tumoral tissue

Background The study of cytotoxic T-lymphocytes (Tcy) has shown increased attention from the scientific community in the last years because of their predictive role in anti-cancer therapy with specific interest in immune check point blocking therapy. However, most of these studies have used bulk or dissociation-based single-cell technologies to draw their biological insights. Lately, new spatial -omics technologies are increasing our knowledge on this population by adding the spatial location of these cells in-situ in the native structure of the tissue. In this study, we have compared the activation of Tcy in reactive and cancerous conditions at single cell level and in the micro-anatomical context of the tissue.

Experimental procedures One tissue micro array slide containing: reactive tonsil, inflammatory liver disease, breast cancer, glioblastoma and melanoma was stained using the COMET™ instrument (Lunaphore Technologies SA) for a multiplex panel of 20 markers. The derived multiplexed images were analyzed using the DISSCOVERY software platform developed by the MILAN Unit at KU Leuven (Belgium). 12/20 markers were specifically aimed at identifying the main cell populations in the tissue (CD11b, CD163, CD20, CD3, CD31, CD4, CD56, CD68, CD8, CK, FOXP3, S100) while the remaining 8 markers were aimed at adding functional information on immune cell types of interest (CD69, HLA-DR, Ki67, LAG3, OX40, PD-1, PD-L1, TIM3).

Results The general activation levels of the Tcy in the reactive conditions were higher than in the three cancer subtypes. When looking at Tcy activation as a function of the distance from the vascular structures (identified via CD31+ endothelial cells), we observed an orderly distribution of activated Tcy around CD31+ endothelial cells with a gradient of increasing exhaustion levels with increasing distance from the vessel in the reactive conditions. In the cancer samples, on the contrary, a patchy disorderly organized pattern of exhausted and activated Tcy was observed around the vessels.

Conclusion The spatial location of inflammatory cells plays a critical role to understand their functional behavior and thanks to technological progress it is now possible to start doing this at scale. The study of the dynamics of exhaustion of Tcy in the tissue will help clarify the interplay between cancer cells and immune environment. These results will be crucial to better select patients who may benefit the most of immune check point blockade.

Citation Format: Maxim De Schepper, Asier Antoranz, Nikolina Dubroja, Giuseppe Floris, Frederik De Smet, Francesca Bosisio. Spatial dynamics of cytotoxic T lymphocyte exhaustion in reactive and tumoral tissue. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6773.

The Upgrade Risk of B3 Lesions to (Pre)Invasive Breast Cancer After Diagnosis on Core Needle or Vacuum Assisted Biopsy. A Belgian National Cohort Study

INTRODUCTION

Flat epithelial atypia (FEA), lobular neoplasia (LN), papillary lesions (PL), radial scar (RS) and atypical ductal hyperplasia (ADH) are lesions of uncertain malignant potential and classified as B3 lesions by the European guidelines for quality assurance in breast cancer screening and diagnosis. Current management is usually wide local excision (WE), surveillance may be sufficient for some. We investigated the upgrade rate of B3 lesions to breast malignancy in a subsequent resection specimen after diagnosis on core needle-or vacuum assisted biopsy (CNB-VAB) in a national population-based series.

METHODS

Using data from the Belgian Cancer Registry (BCR) between January 1, 2013 and December 31, 2016, inclusion criteria were new diagnosis of a B3 lesion on CNB or VAB with subsequent histological assessment on a wider excision specimen. Histological agreement between first- and follow-up investigation was analyzed to determine the upgrade risk to ductal adenocarcinoma in situ (DCIS) or invasive breast cancer (IC) according to the type of B3 lesion.

RESULTS

Of 1855 diagnosed B3 lesions, 812 were included in this study: 551 after CNB-261 after VAB. After diagnosis on CNB and VAB, we found 19.0% and 14.9% upgrade to malignancy respectively. Upgrade risks after CNB and VAB were: FEA 39.5% and 17.6%; LN 40.5% and 4.3%; PL 10.4% and 12.5%; RS 25.7%and 0.0%; ADH 29.5% and 20.0%.

CONCLUSION

Based on the observed upgrade rate we propose three recommendations: first, resection of ADH, and FEA with WE; second, resection of RS and classical LN with therapeutic VAB and further surveillance when radio-pathological correlation is concordant; third, surveillance of PL.

Abstract P3-05-28: Impact of increased adiposity on extended aromatase inhibitor treatment in postmenopausal patients with estrogen receptor positive (ER+) breast cancer: a retrospective analysis of the SOLE trial

Background: The risk of late distant recurrence (≥ 5 years) in post-menopausal patients with ER+ BC remains significant even after standard adjuvant endocrine therapy (ET). Obesity, which has reached high proportions in Western Countries, is one of the modifiable factors that can contribute to BC recurrences. While body mass index (BMI) is an easily available surrogate measure of adiposity, it might not reflect accurately patient adiposity, especially in post-menopausal patients. We therefore hypothesize that mammary adipocyte measurements might better capture the adiposity of the patient. In this study, we retrospectively evaluated the prognostic role of both BMI and adipocyte measurements in the SOLE trial.

Patients & Methods: The SOLE trial (NCT00553410) consisted of 4,884 postmenopausal women with hormone receptor positive, lymph node-positive BC treated with 5 years of letrozole after having completed 4-6 years of adjuvant ET. BMI was available for 3,606 patients with ER+/HER2- BC and categorized according to the WHO classification (underweight: &lt; 18.5, normal weight 18.5 – 24.9, overweight 25 – 29.9, obesity ≥ 30 kg/m2). Considering the small sample size, patients with underweight (n=35) were grouped together with patients with normal weight for the subsequent analyses. We evaluated the association between clinico-pathological characteristics and BMI using Fisher exact test and Kruskal-Wallis test. Given the previously reported association of BMI with distant recurrences (PMID: 21115856), we considered distant-relapse free interval (DRFI) as the main study endpoint. Cox regression analyses were adjusted for histology, chemotherapy (yes/no), type of local therapy, in addition to previously reported clinico-pathological variables (PMID: 29158011). Then, we conducted a stratified case-cohort study consisting of 311 patients (97 with distant relapse-cases) with successful digital assessment of adipocytes on normal mammary adipose tissue sample collected at surgery, as previously described (PMID: 33120083). Stratification factors were treatment arm and type of prior ET. Weighted Cox regression models (PMID: 17554753, 18712477) were used to evaluate prognostic association with adipocyte size (area in µm²) categorized in quartile of the 75th percentile (Q4 vs Q1-3), as done previously (PMID: 33753731).

Results: 1392 (39%) patients were normal weight, 1315 (36%) were overweight and 899 (25%) were obese. Older age at diagnosis, lymph node involvement (≥4), large tumor size and menopausal status were associated with overweight and obesity. After a median follow-up of 84 months, no associations were found between DRFI and BMI in the univariable and multivariable analysis (adjusted HR overweight vs normal=0.99, 95%CI: 0.76 – 1.29, p=0.977 and HR obese vs normal=1.11, 95%CI: 0.84 - 1.47, p=0.425). In the case-cohort study, patients with larger adipocytes had an increased hazard of distant recurrence in the univariable and multivariable analysis (see table 1).

Conclusion: In this study, we did not detect any association between BMI and survival outcomes. We however found that larger mammary adipocytes were independently associated with an increased hazard of distant recurrence. These results suggest that mammary adipocytes, which can be easily evaluated on H&E slides using digital pathology, should be considered as a novel marker to evaluate the risk of late recurrence in patients with breast cancer.

Abstract P5-05-06: ctDNA detection in seven different types of body liquids in patients with metastatic breast cancer

Background. Liquid biopsies represent a less invasive alternative to tissue biopsy to characterize and possibly monitor the disease in patients with metastatic breast cancer. So far, blood remains the most frequently investigated body liquid in this context and the investigations mainly focus on the detection, quantification and characterization of the circulating tumor DNA (ctDNA). However, since blood might not capture the full disease profile, other sources of body liquids may have the potential to complement the information obtained from blood. The aims of the present study are therefore to assess whether: (i) ctDNA can be detected in different types of body liquids, and, (ii) the levels of ctDNA in a given liquid are associated with metastases in specific organs.

Patients and methods. Twelve patients from the post-mortem tissue donation program UPTIDER (NCT04531696) were included in this study. The receptor status of their primary tumor was: estrogen receptor negative, HER2 non-amplified (ER+/HER2-) (n=9), ER-/HER2- (n=2) and ER+/HER2+ (n=1). Median time between inclusion and death of the patient was 1.6 months (Interquartile range: [0.4-3.4]). Seven types of liquids were collected: blood, saliva, ascites, pleural fluid (PFL), cerebrospinal fluid (CSF), pericardial fluid and urine. Fluids were collected at study inclusion (blood, as well as saliva, urine, and ascites whenever possible) and at autopsy (except for saliva). In total, 108 liquid samples were collected and immediately centrifuged according to standard protocols. Cell free DNA (cfDNA) was extracted from the supernatant. All extracted cfDNA as well as germline DNA extracted from the 12 matched buffy coat samples underwent shallow whole genome sequencing. Log2 ratios were computed with CNVkit, and co-segmented per patient using the copynumber R package. Purity and ploidy were assessed by ABSOLUTE. Associations between organ involvement and ctDNA yield were assessed by Wilcoxon rank-sum tests. Samples at study inclusion and at autopsy were considered together unless otherwise specified.

Results. At the sample level, ctDNA could be identified in 54% of the samples. At the patient level, the proportion of liquid types in which ctDNA was detected was highly variable (median: 58%, IQR: 34-77%, Table 1). CtDNA was detected in ascites of all patients when investigated, in 78% of PFL, 73% of CSF, 67% of blood and 37% of pericardial fluid. Only for one patient with invasive lobular carcinoma, ctDNA was detected in saliva and urine, the latter most likely explained by invasion of the bladder. Of note, in 4/12 patients ctDNA could not be identified in blood but was detected in at least one of the other fluids for 3 of these patients. At autopsy, ctDNA levels tended to be higher in PFL, ascites, and CSF in case of pleural, peritoneal, and central nervous system (CNS) metastases respectively, reaching statistical significance only for PFL. In CSF, two patients have CSF ctDNA detected with no documented involvement of the CNS. No brain autopsy was however performed for these patients.

Conclusion. We have shown that ctDNA can be detected in all 7 different body liquids that were investigated in this study. The ctDNA levels in a given liquid can be associated with the presence of metastases in specific organs. Since ctDNA was not detected in 4 of our patients in blood but detectable for 3 of them in other liquids, the evaluation of additional sources of body fluids should be further investigated in patients with metastatic breast cancer. These results therefore open new avenues for the clinical monitoring and characterization of the disease.

Table 1. Summary of ctDNA detection per liquid type at the patient level based on the 108 evaluated samples. Histo.= Histological, ILC= Invasive lobular carcinoma, NA= not available, nr= number, NST= non-special type

Citation Format: François Richard, Tatjana Geukens, Maxim De Schepper, Amena Mahdami, Karen Van Baelen, Marion Maetens, Ha-Linh Nguyen, Anirudh Pabba, Sophia Leduc, Edoardo Isnaldi, Maysam Hajipirloo, Emily Vanden Berghe, Imane Bachir, Sigrid Hatse, Peter Vermeulen, Evy Vanderheyden, Bram Boeckx, Diether Lambrechts, Ann Smeets, Ines Nevelsteen, Kevin Punie, Patrick Neven, Hans Wildiers, Wouter Van Den Bogaert, Elia Biganzoli, Giuseppe Floris, Christine Desmedt. ctDNA detection in seven different types of body liquids in patients with metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-05-06.

Abstract P6-01-47: Stromal tumor infiltrating lymphocytes and pathological complete response in patients with inflammatory breast cancer treated with neoadjuvant chemotherapy

Background: Inflammatory breast cancer (IBC) is a rare (1-5%), but aggressive form of breast cancer (BC), accounting for ~10% of BC mortality. In early setting (M0), standard of care is neoadjuvant chemotherapy (NACT), followed by surgery. Nevertheless, outcome is still relatively poor. Pathological complete response (pCR) after NACT is prognostic in BC in general, and can be predicted by a high percentage of stromal tumor infiltrating lymphocytes (sTIL) in the primary tumor. The predictive value of sTIL in IBC has only been sporadically investigated, often in smaller series. Our aim was to determine which variables, including sTIL, are associated with pCR and to determine the prognostic value of pCR in IBC in a large multicentric, retrospective cohort. Patients & Methods: We included patients with IBC treated with NACT+/- anti-Human Epidermal growth factor Receptor 2 (HER2) therapy, followed by surgery from 10/1996 to 10/2021 in 7 different European hospitals. Clinicopathological variables were collected and central pathological review was performed, including sTIL scoring. This study focused on M0 cases. Considered clinicopathological variables were: age, histology, tumor grade, estrogen receptor status (ER), HER2 status, focality (unifocal vs not), and baseline locoregional nodal status (Table 1). Associations between pCR, clinicopathological variables and sTIL were assessed using Firth’s logistic regression models: Model 1 was adjusted for center, Model 2 additionally included all variables of interest. Similarly, linear regression was used to investigate the association between sTIL and clinicopathological features. Univariable and multivariable Cox regression was used to evaluate the role of pCR on disease free survival (DFS), distant recurrence free survival (DRFS) and overall survival (OS). DFS and DRFS were analyzed considering death without the respective event as competing risk. Results: 494 patients were included. The distribution according to receptor status was: ER-/HER2- (24.3%), ER+/HER2- (34.4%), ER+/HER2+ (13%) and ER-/HER2+ (20.2%). pCR rate was 26% and per receptor status: ER-/HER2- (28%), ER+/HER2- (10%), ER+/HER2+ (42%) and ER-/HER2+ (45%). pCR was associated with grade (G3 vs G1/2, OR =2.79 (1.70 − 4.74), p &lt; .001), ER-status (positive vs negative, OR = 0.39 (0.26 − 0.60), p &lt; .001) and HER2 status (positive vs negative, OR = 3.74 (2.43 − 5.81), p &lt; .001) in Model 1. Only the association with HER2 status remained significant in Model 2 (OR = 5.34 (2.83 − 10.47), p &lt; .001). sTIL was scored for 385 patients. Median sTIL was 5.3% [IQR 2.0%;16.7%] and according to receptor status: ER-/HER2- (10%), ER+/HER2- (2.5%), ER+/HER2+ (6.7%) and ER-/HER2+ (8.3%). Higher sTIL was associated with NST (p = .032), grade 3 (p = .015), and ER-negativity (p = .007) in Model 1. This was no longer significant in Model 2, but the direction of the trends was preserved. sTIL was associated with pCR (5% increment, OR = 1.13 (1.05 − 1.22), p = .002), but no longer after adjustment. No association between pCR and sTIL was found stratifying by receptor status. The median FU was 9.4 years and multivariable Cox regression models revealed that ER+ and HER2+ status and achieving pCR were significantly associated with better DFS, DRFS, and OS (Table 1). Conclusion: Our results indicate that patients with HER2+ tumors have a higher probability of achieving pCR and that pCR has an independent prognostic role in IBC. This is the largest IBC study with centrally scored sTIL, demonstrating that sTIL is associated with pCR but its role as an independent predictor of pCR is still not certain.

Citation Format: Maxim De Schepper, Ha-Linh Nguyen, François Richard, Florence Lerebours, Roman Vion, Florian Clatot, Anca Berghian, Marion Maetens, Sophia Leduc, Edoardo Isnaldi, Chiara Molinelli, Matteo Lambertini, Frederica Grillo, Gabriele Zoppoli, Luc Dirix, Hilde Wuyts, Kevin Punie, Hans Wildiers, Chantal Remmerie, Ann Smeets, Ines Nevelsteen, Patrick Neven, Anne Salomon, Denis Larsimont, Caroline Duhem, Patrice Viens, François BERTUCCI, Elia Biganzoli, Peter Vermeulen, Giuseppe Floris, Christine Desmedt. Stromal tumor infiltrating lymphocytes and pathological complete response in patients with inflammatory breast cancer treated with neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-47.

Abstract HER2-16: HER2-16 Inter-lesion heterogeneity of HER2-status in metastatic breast cancer: possible implications for treatment with anti-HER2 antibody-drug conjugates

Background. Trastuzumab deruxtecan (T-DXd) has shown promising activity in patients with HER2-low metastatic breast cancer. As the HER2-status can vary between the primary and its corresponding metastases, treatment decisions should ideally be based on HER2 assessment of a recent biopsy. However, limited data is available on intra-patient inter-metastatic heterogeneity in HER2-status, affecting representability of a single biopsy and potential therapeutic options and outcome. We therefore assessed HER2 status on multiple metastases from patients with primary ER-positive/HER2-non-amplified breast cancer in our prospective post-mortem tissue donation program UPTIDER (NCT04531696). Methods. Ninety-one metastatic samples retrieved during the autopsies of 6 patients (range: 13–16/patient) and their respective primary tumours were immunohistochemically (IHC) stained for HER2 (HercepTestTM, RTU, ISO-15189 accredited) in our institution. Consensus scoring was performed between two pathologists according to ASCO/CAP 2018 guidelines. The observers were blinded for patient ID. Reflex fluorescence in situ hybridization (FISH) testing was performed for samples with IHC score of 2+. HER2 status was categorized as HER2-zero (IHC 0), HER2-low (IHC 1+ or IHC 2+ with negative FISH), or HER2-positive (IHC 3+ or IHC 2+ with positive FISH). To assess stability of the performance of IHC scoring in the post-mortem setting, an additional 13 samples taken from 3 metastases at regular (every 1.5h) time intervals during the autopsy underwent HER2 IHC scoring. Results. Evaluation of HER2-status in the primary tumour showed 2 patients with HER2-zero disease and 4 with HER2-low disease. A discordance between HER2 status of the metastases and their respective primary was seen in all patients. Not a single lesion was found to be HER2-positive. For every patient, at least one HER2-low metastasis was observed, with the percentage being highly variable between patients and ranging between 7 and 100%. No association was observed between HER2 status and organ site: HER2-low as well as HER2-zero lesions were found in all organs evaluated in at least 4 patients (liver, bone, pleura, lymph nodes). For 5 patients, multiple lesions within the liver were evaluated: while HER2-zero versus HER2-low status was concordant in those lesions in 4 patients, a mix of HER2 IHC scores was seen in 3 of them. IHC scores were stable over time for tumour lesions assessed repeatedly. Discussion. Important inter-lesion heterogeneity in terms of HER2-low status was observed in patients with primary ER-positive/HER2-non-amplified breast cancer participating to our post-mortem tissue donation program. This observed heterogeneity is unlikely to be due to post-mortem changes in HER2 expression. HER2-low status was found in at least one distant lesion in all patients, complicating therapeutic decision-making based on a single biopsy. Of note, IHC 1+ and 2+ scores varied between metastases of each patient too, making assessment on a single biopsy less reliable for stratification in clinical trials. Further assessment on samples from UPTIDER-patients with ER-negative disease is currently ongoing and results will be available to be presented.

Citation Format: Tatjana Geukens, Maxim De Schepper, François Richard, Marion Maetens, Karen Van Baelen, Amena Mahdami, Ha-Linh Nguyen, Edoardo Isnaldi, Sophia Leduc, Anirudh Pabba, Imane Bachir, Freya Mertens, Sara Vander Borght, Ann Smeets, Ines Nevelsteen, Kevin Punie, Patrick Neven, Hans Wildiers, Wouter Van Den Bogaert, Giuseppe Floris, Christine Desmedt. HER2-16 Inter-lesion heterogeneity of HER2-status in metastatic breast cancer: possible implications for treatment with anti-HER2 antibody-drug conjugates. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-16.

Abstract PD4-06: PD4-06 Obesity-associated changes in transcriptomic profile and immune landscape of primary breast cancer revealed by bulk and single-cell gene expression data

Background: Breast cancer (BC) is one of the cancer types recognized as an obesity-associated disease. Current understandings of molecular mechanisms underlying the BC-obesity connection however largely came from experimental models while systematic investigation of the impact of obesity on BC biology in large patient series is still lacking. The purpose of this study is to discover changes in the transcriptomic profile of primary BC according to patients’ body mass index (BMI). Data and Methods: Bulk and single-cell gene expression data from treatment-naïve primary breast tumors from non-underweight patients were retrieved from the MINDACT trial (NCT00433589; N = 1481) and the pre-treatment cohort of the BioKey trial (NCT03197389, N = 36), respectively. Three categories were considered for BMI: lean, overweight and obese. The main analyses focused on the invasive carcinoma of no special type (NST) estrogen receptor-positive/HER2-negative (ER+/HER2-, N_bulk = 735, N_single-cell(sc) = 10) and NST ER-/HER2- (N_bulk = 118, N_sc = 15) subgroups. The bulk expression data was subjected to differential gene expression analyses according to BMI which was adjusted for menopausal status and tumor grade, then followed by gene set enrichment analyses. Clustering and cluster annotation were performed on the single-cell profiling data before differentially expressed genes according to BMI were identified for each of the present cell types. Results: Obesity-associated differences in the transcriptomic profile of breast tumors, which were subtle but potentially indicative of a biological relationship, were revealed by the bulk data. In both investigated subgroups, tumors from obese patients were shown to be enriched in cell cycle hallmarks. In ER-/HER2- tumors, adiposity further increased MYC signaling. We also observed different obesity-associated changes according to the ER status. Among ER+/HER2- tumors, those from obese patients were enriched in hallmarks related to inflammatory response compared to those from lean patients. In contrast, these hallmarks appeared to be enriched in the ER-/HER2- tumors from lean patients. Our investigation of the single-cell data further revealed shifts in the cell composition of tumor tissue and cell type-specific transcriptomic differences according to BMI which were more pronounced than those detected from the bulk data. ER+/HER2- tumors from obese patients have a higher frequency of immunosuppressive and pro-tumoral cell subpopulations such as dendritic cells (DC) enriched in immunoregulatory molecules (p = .03), LYVE1+ macrophages (p = .02) and myofibroblasts (p = .03) than those from lean patients. Overexpression of Cyclin D1 and CD24 was found in cancer cells in ER+/HER2- tumors from obese patients. A reduction in anti-tumor immune responses was evident with downregulation of multiple interferons in CD8+ and CD4+ T cells as well as B cells. We observed in the ER-/HER2- subgroup increased infiltration of plasmacytoid DC (p = .01), CCL2+ macrophages (p = .01) in tumors from obese versus lean patients, while fibroblasts showed an opposite tendency. Additionally, significant obesity-associated downregulation of major histocompatibility complex (MHC) molecules class I in cancer cells and MHC class II molecules in B cells could be suggestive of deficient antigen presentation and activation of cytotoxic and helper T cells. Conclusion: We highlighted the impact of obesity on the remodeling of tumor and tumor microenvironment which might generally lead to a suppression of anti-tumor immune responses, albeit potentially via diverse axes according to the ER status. Although investigation on a larger cohort is warranted, our current results suggest that obesity-associated transcriptomic changes in BC could be highly cell type-specific, hence we recommend single-cell approaches in addition to spatial multi-omics analysis to further elucidate the interplay between obesity and BC.

Citation Format: Ha-Linh Nguyen, Tatjana Geukens, Marion Maetens, Karen Van Baelen, Maxim De Schepper, Coralie Poncet, Mauro Delorenzi, Marjanka K. Schmid, Emiel Rutgers, Laura Van ’t Veer, Martine Piccart, Fatima Cardoso, Giuseppe Viale, Ayse Bassez, Hanne Vos, Patrick Neven, Ines Nevelsteen, Kevin Punie, Hans Wildiers, Giuseppe Floris, Diether Lambrechts, Ann Smeets, Elia Biganzoli, François Richard, Christine Desmedt. PD4-06 Obesity-associated changes in transcriptomic profile and immune landscape of primary breast cancer revealed by bulk and single-cell gene expression data [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD4-06.

Abstract P3-05-40: Association of body mass index with clinicopathological features and survival in patients with primary ER+/HER2- invasive lobular breast cancer

Background: Invasive lobular carcinoma (ILC) represents up to 15% of all breast carcinomas. The majority of ILC express the estrogen receptor (ER) and have no amplification/overexpression of the human epidermal growth factor receptor 2 (HER2). A high body mass index (BMI) has been associated with an increased risk of developing ILC in postmenopausal women, similar to what is seen for breast cancer of no special type (NST). It is however unknown if BMI impacts the clinicopathological features and the prognosis of ILC.

Methods: We performed a multicentric retrospective study in 5 European centers of patients diagnosed between January 2000 and December 2020 with ER+/HER2- non-metastatic pure (i.e., not mixed) ILC. Patient and tumor characteristics and event-related data were collected. BMI was categorized into underweight (≤18.5kg/m2), lean (&gt;18.5kg/m2 and &lt; 25kg/m2), overweight (≥25kg/m2 and &lt; 30kg/m2) and obese (≥30kg/m2). The association of BMI as either a continuous or a categorical variable with clinicopathological variables was assessed using linear regression or ordinal logistic regression, respectively. Median follow-up was calculated using the reverse Kaplan-Meier estimator. Survival analyses using univariable (stratified by center) and multivariable (adjusted for all included variables and stratified by center) Cox regression were performed to evaluate the association of BMI with disease free survival (DFS), distant recurrence free survival (DRFS) and overall survival (OS). DFS and DRFS were analyzed in the presence of death without event as the competing risk.

Results: The data of 2476 patients were collected and BMI was available for 2346 patients. In total, 1299 (55%) patients were lean, 638 (27%) overweight and 339 (14%) obese. Underweight patients only represented 3% of all patients and were thus excluded from further analyses. A higher age at diagnosis, higher grade, larger tumor size, nodal involvement and multifocality were significantly associated with higher BMI (Table 1). The median follow-up was 8,5 years (interquartile range 59.24 – 142.13 months). In univariable analysis, higher BMI was associated with worse survival outcomes (Table 2). However, this association was not seen in multivariable analysis while grade, tumor size and nodal involvement were still prognostic for all endpoints. Similar results were seen with BMI as a continuous variable.

Conclusion: Larger tumors and nodal involvement were more likely to be found in patients with ER+/HER2- ILC with higher BMI which might be explained by a delayed diagnosis in these patients. Higher grade also seemed to be associated with higher BMI. In multivariable analyses, BMI was not found to be an independent prognostic factor. Tumor grade, tumor size, and nodal status remained strongly prognostic for survival outcomes in multivariable survival analyses which is consistent with their known prognostic importance in luminal tumors. We hypothesize that the prognostic effect of BMI is mediated through these variables for patients with ER+/HER2- ILC.

Table 1. Association of clinicopathological features of ER+/HER2- ILC with categorical BMI.

Table 2. Association of categorical BMI and other clinicopathological features of ER+/HER2- ILC with survival.

Citation Format: Karen Van Baelen, Ha-Linh Nguyen, François Richard, Anne-Sophie Hamy, Aullène Toussaint, Fabien Reyal, Anne Salomon, Luc Dirix, Peter Vermeulen, Hilde Wuyts, Maria Karsten, Adam D. Dordevic, Guilherme Nader Marta, Evandro de Azambuja, Christos Sotiriou, Denis Larsimont, Ottavia Amato, Marion Maetens, Maxim De Schepper, Tatjana Geukens, Sileny Han, Thaïs Baert, Kevin Punie, Hans Wildiers, Chantal Remmerie, Ann Smeets, Ines Nevelsteen, Giuseppe Floris, Elia Biganzoli, Patrick Neven, Christine Desmedt. Association of body mass index with clinicopathological features and survival in patients with primary ER+/HER2- invasive lobular breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-40.

Abstract P3-05-35: The impact of parity and age of first full term pregnancy on the prevalence of invasive lobular carcinoma in patients with breast cancer

Background: The impact of reproductive factors on breast cancer has proven to be complex. The risk for estrogen receptor positive/HER2-negative (ER+/HER2-) breast cancer is estimated to be transiently augmented in the years after giving birth (up to 20 years) while later in life high parity and early first full-term pregnancy (1st FTP) seem to protect against ER+/HER2- breast cancer (BC). Invasive lobular carcinomas (ILC) represents the second most common histological subtype of BC and &gt;90% are ER+/HER2-. In this study, we aimed at investigating whether parity and age at 1st FTP are associated with: 1) the prevalence of ER+/HER2- pure ILC (i.e., not mixed) in an ER+/HER2- BC cohort (overall and according to the age at breast cancer diagnosis), and, 2) standard clinical and pathological features of pure ILC.

Patients and methods: We performed a single center retrospective study in UZ Leuven, Belgium of patients diagnosed with non-metastatic ER+/HER2- breast cancer between January 2000 and November 2020. Both patient and tumor characteristics were collected from clinical files. Firth’s logistic regression was performed to investigate the association of BC histology (pure ILC vs all other BC histological subtypes = control group) with parity (yes vs. no and nulliparous, 1 child, 2 children, &gt;2 children) in univariable models and multivariable models adjusted for age group at diagnosis (&lt; 30, 31-40, 41-50, 51-60, 61-70, &gt;70), age at 1st FTP (continuous and per age group: &lt; 21, 21-25, 26-30, &gt;30), Interval between 1st FTP and diagnosis (continuous), year of birth and BMI. Analyses were done in the overall group as well as per age group at diagnosis. Similarly, regression analyses were performed in patients with ER+/HER2- ILC to assess the association of parity (yes vs. no and nulliparous, 1 child, 2 children, &gt;2 children) with the following variables: age at diagnosis, BMI, histological grade, tumor size, nodal involvement and progesterone receptor positivity.

Results: 7360 patients were included of which 1121 (15.2%) were diagnosed with pure ER+/HER2- ILC, the remaining 6239 (84.8%) patients were considered as the control group. Overall, in multivariable analyses, parity with &gt;2 children was associated with a higher prevalence of pure ILC as compared to uniparous patients (odds ratio, OR 1.257, 95CI 1.039-1.521, p= 0.019). No significant association was seen for age at 1st FTP and interval 1st FTP – diagnosis. The subgroup analyses per age group are summarized in Table 1. Only for the age group 41-50, an increased age 1st FTP was associated with an increased prevalence of pure ILC. In patients with pure ER+/HER2- ILC, nulliparous women were less likely to have a progesterone receptor (PR)-positive tumor as compared to parous women (OR 0.477, 95CI 0.224-0.907, p= 0.022). No other significant associations were seen for clinicopathological features between nulliparous and parous women, and between uniparous and multiparous women in the overall cohort nor any age group.

Conclusions: Within an ER+/HER2- breast cancer cohort, higher parity seems to be associated with a higher prevalence of pure ILC, which is especially seen in the patients diagnosed with breast cancer between the age of 51 and 60. Increased age at the 1st FTP only seems to increase the incidence of ILC in the age group 41-50. With the exception of nulliparous women having less PR positive tumors, parity does not seem to affect the clinicopathological features of ER+/HER2- pure ILC.

Table 1: subgroup analyses per age group of association of histology (pure ILC vs control group) with parity, age 1st FTP and interval 1st FTP – diagnosis

Citation Format: Karen Van Baelen, Ha-Linh Nguyen, François Richard, Maja Vangoitsenhoven, Giuseppe Floris, Hans Wildiers, Kevin Punie, Ann Smeets, Ines Nevelsteen, Frédéric Amant, Sileny Han, Thaïs Baert, Patrick Neven, Christine Desmedt. The impact of parity and age of first full term pregnancy on the prevalence of invasive lobular carcinoma in patients with breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-35.

Abstract P6-14-14: Advancing research on metastatic breast cancer: the UPTIDER post-mortem tissue donation program

Background. Research in metastatic breast cancer is hampered by limited sample availability. Post-mortem tissue donation programs can help to overcome this problem but are logistically challenging and have thus far mainly focused on histopathological and genomic research. We here present the UPTIDER program (NCT04531696), aimed at the multilevel characterization of advanced breast cancer and generation of tumour models. Patients and Methods. Patients with stage IV breast cancer receiving their last line(s) of treatment are eligible for participation. Blood, urine and saliva samples are collected upon inclusion. Upon death, a post-mortem MRI (when possible) followed by a rapid autopsy is performed. Liquid biopsies from all body fluids and tissue samples from all macroscopically identified metastatic sites are collected. Samples are processed as mirrored biopsies in different conditions, such as fresh frozen for omics analyses, formalin fixed paraffin-embedded for histopathology, and slowly frozen in freezing medium or fresh for generation of xenograft and organoid models. Results. Since approval by the local Ethical Committee in November 2020, 22 patients have been enrolled and 15 autopsies have been performed. Mean interval between death and start of autopsy was 3h (range 2-6h), mean duration of the autopsies was 6h (4-9h). A post-mortem MRI was performed in 6 patients. Peripheral blood, central blood and bone marrow were collected from all patients; urine, ascites, cerebrospinal, pericardial and pleural fluid all in more than 2/3 of patients. On average, 232 (range 90-406) tissue samples of which 164 (45-303) pathological from 42 (15 – 79) metastases were collected for each patient. Most often sampled metastatic sites were lymph nodes, liver, bones, pleura and peritoneum. Samples from the primary tumour could be retrieved from all patients, either during the autopsy (n=6) or from historical archives. In total, 133 tumour samples were sent to collaborating partners for patient-derived xenograft creation. Already some have been successfully established and stored, including models derived from a patient with invasive lobular carcinoma (ILC) and one with metaplastic squamous cell carcinoma. When correlating microscopic and macroscopic findings, patients could largely be divided into three main categories. Eleven patients presented with overt and extensive disease burden, often characterized by diffuse visceral, pleural, peritoneal, bone and lymph node involvement. Two patients, both with ILC, presented with underestimated yet extensive disease burden. While gross examination and cross sectioning of organs did not reveal clear involvement, microscopical invasion of stomach and liver, amongst others, was found. Lastly, limited disease burden was seen in two patients, both with leptomeningeal involvement. In those patients, massive tumoral infiltration in the subarachnoid space and along the blood-brain barrier was seen microscopically, with no grey matter invasion. Conclusion. We successfully launched a new and comprehensive post-mortem tissue donation program for patients with metastatic breast cancer, enrolling ~ 1 patient per month. Post-mortem tumour samples already resulted in successful establishment of some patient-derived xenografts. From a clinical point of view, vast underestimation of the disease extent on imaging during life as well as macroscopically during the autopsy was observed in some patients with metastatic ILC. For patients with leptomeningeal metastasis, we showed that the highly aggressive nature of their disease might be explained by extensive meningeal infiltration disrupting the blood-brain barrier. Further insights into disease progression and heterogeneity will be generated by the ongoing multi-omics analyses.

Citation Format: Tatjana Geukens, Maxim De Schepper, Karen Van Baelen, François Richard, Marion Maetens, Amena Mahdami, Ha-Linh Nguyen, Edoardo Isnaldi, Anirudh Pabba, Sophia Leduc, Imane Bachir, Maysam Hajipirloo, Emily Vanden Berghe, Sigrid Hatse, Eleonora Leucci, Maria Francesca Baietti, Georgios Sflomos, Cathrin Brisken, Patrick Derksen, Colinda Scheele, Vincent Vandecaveye, Ann Smeets, Ines Nevelsteen, Kevin Punie, Patrick Neven, Elia Biganzoli, Hans Wildiers, Wouter Van Den Bogaert, Giuseppe Floris, Christine Desmedt. Advancing research on metastatic breast cancer: the UPTIDER post-mortem tissue donation program [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-14-14.

A palmitate-rich metastatic niche enables metastasis growth via p65 acetylation resulting in pro-metastatic NF-κB signaling

Metabolic rewiring is often considered an adaptive pressure limiting metastasis formation; however, some nutrients available at distant organs may inherently promote metastatic growth. We find that the lung and liver are lipid-rich environments. Moreover, we observe that pre-metastatic niche formation increases palmitate availability only in the lung, whereas a high-fat diet increases it in both organs. In line with this, targeting palmitate processing inhibits breast cancer-derived lung metastasis formation. Mechanistically, breast cancer cells use palmitate to synthesize acetyl-CoA in a carnitine palmitoyltransferase 1a-dependent manner. Concomitantly, lysine acetyltransferase 2a expression is promoted by palmitate, linking the available acetyl-CoA to the acetylation of the nuclear factor-kappaB subunit p65. Deletion of lysine acetyltransferase 2a or carnitine palmitoyltransferase 1a reduces metastasis formation in lean and high-fat diet mice, and lung and liver metastases from patients with breast cancer show coexpression of both proteins. In conclusion, palmitate-rich environments foster metastases growth by increasing p65 acetylation, resulting in a pro-metastatic nuclear factor-kappaB signaling.

Abstract P2-11-18: Serum methylmalonic acid concentrations at breast cancer diagnosis are not associated with distant metastases

Introduction: Methylmalonic acid (MMA), a metabolite and by-product of propionate metabolism, promotes breast cancer (BC) progression in mice via the transforming growth factor-beta (TGFβ) signaling pathway (Gomes et al, Nature 2020). It is currently unknown if this effect also exists in patients with BC. Objectives: To investigate the association between baseline serum MMA concentrations in patients at BC diagnosis and development of distant metastases via a matched case-control study. Methods: We included 32 patients with early Luminal B-like BC (Lumb, median age 62.4y) and 52 patients with early triple-negative BC (TNBC, median age 50.5y) who developed distant metastases within 5 years. They were matched to an equal number of early BC patients with at least 5 years of follow-up (median age 62.2y for Lumb and 50.5y for TNBC) who did not develop distant metastases with at least 5 years of follow-up. Matching was performed based on age at diagnosis date (± 5y), tumor stage, and treatment received ((neo)adjuvant chemotherapy and radiotherapy, yes/no). Serum MMA concentrations were determined by liquid chromatography with tandem mass spectrometry (LC-MS-MS). Summary statistics, paired analyses, and multiple conditional logistic regression analyses were performed with and without adjusting for potential covariates (age, kidney function, and tumor stage). Results: Baseline serum MMA at BC diagnosis significantly correlated with age (rs=0.35, p=.005 in Lumb; rs=0.35, p=.0003 in TNBC), and negatively correlated with kidney function assessed by estimated glomerular filtration rate (eGFR, rs= -0.42, p=.0005 in Lumb; rs= -0.32, p=.0009 in TNBC). MMA concentrations at diagnosis were not associated with distant metastases in either subtype, after adjusting for kidney function, age, and tumor stage (all p&gt;.05). Next, we categorized BC cases in the public TCGA (n=174 for Lumb; n=140 for TNBC), METABRIC (n=461 for Lumb; n=199 for TNBC), and GSE25066 (n=78 for Lumb; n=182 for TNBC) database according to their 5-year metastatic status, and analyzed the TGFβ signaling pathway activity of primary BC. Like MMA concentrations, a gene expression signature of TGFβ signaling was not associated with distant metastases in patients with BC. Conclusion: Baseline serum MMA concentrations and a gene signature for TGFβ signaling at BC diagnosis are not associated with distant metastases among patients with Lumb and TNBC subtypes.

Citation Format: Qi Wu, Sigrid Hatse, Juan F. García, Patricia Altea-Manzano, Jaak Billen, Mélanie Planque, Anke Vandekeere, Yentl Lambrechts, François Richard, Annouschka Laenen, Kevin Punie, Patrick Neven, Ines Nevelsteen, Giuseppe Floris, Christine Desmedt, Ana Gomes, Sarah-Maria Fendt, Hans Wildiers. Serum methylmalonic acid concentrations at breast cancer diagnosis are not associated with distant metastases [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-11-18.

Abstract P4-03-20: Association between reproductive factors (parity and age first full term birth) and the frequency of estrogen receptor negative breast cancer according to age at diagnosis

Background: The frequency of early estrogen receptor (ER)-negative breast cancers (BC) decreases with increasing age at diagnosis (Partridge P, JCO 2016). Giving birth is generally considered a protective factor for the occurrence of BC in a woman’s lifetime. However, for up to more than 20 years following childbirth, BC risk may be higher. This appears to be due to an increase in hormone receptor-positive BC, especially in women older at the time of 1st childbirth (Nichols HB, Ann Int Med 2019). This means that the ER-negative BC are relatively less frequent in these 2 decades after delivery. In this study, we aimed at retrospectively investigating the impact of parity and age at first full term pregnancy (FFTP) on the frequency of ER-negative BC according to the age at diagnosis in a large institutional cohort of patients diagnosed with BC.

Patients and Methods: We considered all patients diagnosed and/or treated with early BC in UZ Leuven between January 2000 and November 2020. ER-negativity was defined as &lt; 1% positive cells. Age at diagnosis was subdivided in categories of 5 years. Parous women could be having a low (1 or 2 children) or high parity (&gt; 2 children) and age of FFTP was arbitrarily divided into &lt; or ≥ 27 years of age. BMI was considered a possible confounder and was corrected for. A logistic regression model was used for data analysis with ER-negative status as binary outcome and FFTP class and multiparity as explanatory variables. To test whether the difference in ER-negative proportions between FFTP classes depends on multiparity, we modelled the interaction between multiparity and FFTP class.

Results: We included 9955 consecutive female patients after excluding missing values. 8358 out of 9955 women had at least 1 child (84%). In our study population, parity as such was not an independent variable for BC subtype. Women with a FFTP ≥ 27y as compared to those with a FFTP &lt; 27y were less likely to have an ER-negative BC. The p-value for the interaction term between high parity (&gt;2 children) and FFTP class equals p= 0.0044. Hence, there is statistical evidence to suggest that the differences between FFTP categories with regards to ER-negative BC may depend on multiparity. Table 1 shows a lower incidence of ER-negative BC in the FFTP ≥ 27y group compared to the FFTP &lt; 27y group in case of high parity. Table 2 shows the absolute proportion. These results seem to be independent of BMI.

Conclusion: Women with a FFTP at 27 years of age or older and more than 2 children have proportionally less ER-negative type breast cancers as compared to women with a FFTP before 27 years of age. This difference between FFTP classes is not observed in absence of high parity.

Table 1: effect of FFTP class by multiparity

Table 2: proportion of ER-negative breast cancer subtype

Citation Format: Maja Vangoitsenhoven, Evert Theys, Karen Van Baelen, Annouschka Laenen, Christine Desmedt, Giuseppe Floris, Hans Wildiers, Kevin Punie, Sileny Han, Thaïs Baert, Frédéric Amant, Ann Smeets, Ines Nevelsteen, Rani Vanhoudt, Patrick Neven. Association between reproductive factors (parity and age first full term birth) and the frequency of estrogen receptor negative breast cancer according to age at diagnosis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-03-20.

Abstract P4-01-29: Ribociclib plus letrozole alters the immune subset composition in older (≥70 yrs.) patients with HR+/HER2- metastatic breast cancer

Background The combination of CDK4/6 inhibitors and endocrine therapy is the current standard first-line therapy for patients with HR+/HER2- metastatic breast cancer (mBC). Preliminary data suggest that CDK4/6 inhibitors not only induce tumor response by blocking CDK-dependent cell growth but that they can also alter the host immune function and stimulate tumor cell-directed immunity. However, clinical data are scarce, and no data exist about the impact of age and frailty, which are known to impact host immunity (immunosenescence). Materials and methods This prospective ongoing study is evaluating the efficacy and toxicity of the CDK4/6 inhibitor ribociclib and letrozole in older (≥ 70 years) patients with HR+/HER2- mBC (RIBOB, NCT03956654). In the associated blood biomarker sub-study, we investigate the impact of ribociclib and letrozole on the immune subset composition. Immune cell subsets were analyzed using flowcytometry (BD FACSVerse™) of peripheral blood mononuclear cells isolated at baseline (before ribociclib administration) and after three months of ribociclib treatment. In total, six multicolor flow cytometry staining panels were set up to investigate the changes in the immune cell subsets (CD4+ T-cell subsets, CD8+ T-cell subsets, general immune cell subsets, T-regulatory cell subsets, T-cell activation status subsets, and myeloid-derived suppressor cells subsets). Frailty status was assessed at baseline using the G8 screening tool (range score: 0-17) as a proxy. The paired t-test and matched-pairs Wilcoxon signed-rank test are used to evaluate changes in immune subset composition between baseline and after three months. The unpaired t-test and Mann-Whitney U test are used to evaluate differences in immune subset composition between frail and fit patients. Results Immune cell subset distribution and evolution were available for 15 older patients (median age: 77 yrs.; IQR 74-83), 4 considered fit (G8-score &gt;14), and 11 frail (G8-score ≤14). Firstly, we analyzed the difference in immune subset composition between baseline and three months for the whole cohort. There was a significant increase of naïve T-regulatory cells (p=0.0012) and a significant increase in CD8+ T-cell activation indicated by an upregulation of HLA-DR+ (p=0.0055) and CD38+ (p=0.0203). Secondly, the difference in immune subset composition between fit and frail persons was assessed showing a lower activation status of CD4+ and CD8+ T-cell subsets in frail persons at baseline, as assessed by several activation markers: CD4+PD1+ (p=0.0051), CD4+PD1+CD69+ (p=0.0013), CD8+PD1+ (p=0.0073), and CD8+PD1+CD69+ (p=0.0339). These significant differences between fit and frail disappeared after three months, largely because of increased T-cell activation in the frail subset. Conclusion Ribociclib plus letrozole treatment for three months results in an upregulation of the T-regulatory cells’ naïve subset, suggesting an expansion of the T-cell repertoire, which is compatible with immune cell activation. Furthermore, the activation status of the CD8+ T-cells was upregulated. These observations confirm recent findings reported by Scirocchi F. et al. (Lancet, 2022). In addition, frail older patients show a lower baseline T-cell activation status compared to fit older patients but seem to have increased T-cell activation after treatment exposure. In the future, correlations with treatment response will be evaluated when follow-up data matures. Our data encourage the further assessment of immune cell modulation in combination with CDK4/6 inhibitors in the treatment of patients with metastatic breast cancer.

Citation Format: Yentl Lambrechts, Sigrid Hatse, Cindy Kenis, Lore Decoster, Evandro de Azambuja, Guy Jerusalem, Patrick Neven, Lissandra Dal Lago, Hannelore Denys, Peter Vuylsteke, Frank Cornelis, Kevin Punie, Giuseppe Floris, Christine Desmedt, Annouschka Laenen, Noam Pondé, Hans Wildiers. Ribociclib plus letrozole alters the immune subset composition in older (≥70 yrs.) patients with HR+/HER2- metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-29.

ONEST (Observers Needed to Evaluate Subjective Tests) Analysis of Stromal Tumour-Infiltrating Lymphocytes (sTILs) in Breast Cancer and Its Limitations

Tumour-infiltrating lymphocytes (TILs) reflect antitumour immunity. Their evaluation of histopathology specimens is influenced by several factors and is subject to issues of reproducibility. ONEST (Observers Needed to Evaluate Subjective Tests) helps in determining the number of observers that would be sufficient for the reliable estimation of inter-observer agreement of TIL categorisation. This has not been explored previously in relation to TILs. ONEST analyses, using an open-source software developed by the first author, were performed on TIL quantification in breast cancers taken from two previous studies. These were one reproducibility study involving 49 breast cancers, 23 in the first circulation and 14 pathologists in the second circulation, and one study involving 100 cases and 9 pathologists. In addition to the estimates of the number of observers required, other factors influencing the results of ONEST were examined. The analyses reveal that between six and nine observers (range 2-11) are most commonly needed to give a robust estimate of reproducibility. In addition, the number and experience of observers, the distribution of values around or away from the extremes, and outliers in the classification also influence the results. Due to the simplicity and the potentially relevant information it may give, we propose ONEST to be a part of new reproducibility analyses.

Comparison of the genomic alterations present in tumor samples from patients with metastatic inflammatory versus non-inflammatory breast cancer reveals AURKA as a potential treatment target

Inflammatory breast cancer (IBC) is a rare but aggressive subtype of breast cancer, mainly characterized using primary tumor samples. Here, using public datasets, we compared the genomic alterations in primary and metastatic samples from patients with metastatic IBC versus patients with metastatic non-IBC. We observed a higher frequency of AURKA amplification in IBC. We further showed that AURKA amplification was associated with increased AURKA mRNA expression, which we demonstrated was higher in IBC. Finally, higher protein expression of AURKA was associated with worse prognosis in patients with IBC. These findings deserve further investigation given the existence of AURKA-inhibitors.

Cancer immunotherapies transition endothelial cells into HEVs that generate TCF1+ T lymphocyte niches through a feed-forward loop

The lack of T cell infiltrates is a major obstacle to effective immunotherapy in cancer. Conversely, the formation of tumor-associated tertiary-lymphoid-like structures (TA-TLLSs), which are the local site of humoral and cellular immune responses against cancers, is associated with good prognosis, and they have recently been detected in immune checkpoint blockade (ICB)-responding patients. However, how these lymphoid aggregates develop remains poorly understood. By employing single-cell transcriptomics, endothelial fate mapping, and functional multiplex immune profiling, we demonstrate that antiangiogenic immune-modulating therapies evoke transdifferentiation of postcapillary venules into inflamed high-endothelial venules (HEVs) via lymphotoxin/lymphotoxin beta receptor (LT/LTβR) signaling. In turn, tumor HEVs boost intratumoral lymphocyte influx and foster permissive lymphocyte niches for PD1^- and PD1⁺TCF1⁺ CD8 T cell progenitors that differentiate into GrzB⁺PD1⁺ CD8 T effector cells. Tumor-HEVs require continuous CD8 and NK cell-derived signals revealing that tumor HEV maintenance is actively sculpted by the adaptive immune system through a feed-forward loop.

Abstract A34: Therapeutic induction of High Endothelial Venules in cancer generates TCF1+ lymphocyte niches

The lack of T-cell infiltrates is a major obstacle to effective immunotherapy in cancer. Conversely, the formation of tumor-associated tertiary-lymphoid-like structures (TA-TLS), which are the local site of humoral and cellular immune responses against cancers, are associated with good prognosis and have recently been detected in Immune Checkpoint Blockade (ICB)-responding patients. However, how these lymphoid aggregates develop remains poorly understood. By employing scRNA sequencing, endothelial fate mapping, and multiplex immunohistochemistry, we demonstrate that antiangiogenic immune-modulating therapies evoke the transition of postcapillary venules into inflamed high endothelial venules (HEV), which predominantly generate permissive TA-TLS-like lymphocyte niches. These HEV+ immune niches entail PD1neg and PD1+TCF1+CD8+ progenitor cells that differentiate into cytotoxic TCF1neg TIM3+ PD1+ CD8 effector cells and migrate into the tumor core. Congruently, TU-HEV signatures correlate with response to ICB therapies in several human tumor types. In line with these observations, TU-HEVs require continuous CD8 and NK cell-derived lymphotoxin signals revealing that tumor-HEV maintenance is actively sculpted by the immune system through a feed-forward loop.

Citation Format: Gerlanda Vella, Yichao Hua, Florian Rambow, Elizabeth Allen, Asier Antoranz Martinez, Pascal Merchiers, Francesca Bosisio, Giuseppe Floris, Akira Takeda, Sirpa Jalkanen, Maija Hollmén, Jean-Christophe Marine, Susan Schlenner, Gabriele Bergers. Therapeutic induction of High Endothelial Venules in cancer generates TCF1+ lymphocyte niches [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr A34.

Histopathological growth patterns of liver metastasis: updated consensus guidelines for pattern scoring, perspectives and recent mechanistic insights

The first consensus guidelines for scoring the histopathological growth patterns (HGPs) of liver metastases were established in 2017. Since then, numerous studies have applied these guidelines, have further substantiated the potential clinical value of the HGPs in patients with liver metastases from various tumour types and are starting to shed light on the biology of the distinct HGPs. In the present guidelines, we give an overview of these studies, discuss novel strategies for predicting the HGPs of liver metastases, such as deep-learning algorithms for whole-slide histopathology images and medical imaging, and highlight liver metastasis animal models that exhibit features of the different HGPs. Based on a pooled analysis of large cohorts of patients with liver-metastatic colorectal cancer, we propose a new cut-off to categorise patients according to the HGPs. An up-to-date standard method for HGP assessment within liver metastases is also presented with the aim of incorporating HGPs into the decision-making processes surrounding the treatment of patients with liver-metastatic cancer. Finally, we propose hypotheses on the cellular and molecular mechanisms that drive the biology of the different HGPs, opening some exciting preclinical and clinical research perspectives.

Incorporating progesterone receptor expression into the PREDICT breast prognostic model

BACKGROUND

Predict Breast (www.predict.nhs.uk) is an online prognostication and treatment benefit tool for early invasive breast cancer. The aim of this study was to incorporate the prognostic effect of progesterone receptor (PR) status into a new version of PREDICT and to compare its performance to the current version (2.2).

METHOD

The prognostic effect of PR status was based on the analysis of data from 45,088 European patients with breast cancer from 49 studies in the Breast Cancer Association Consortium. Cox proportional hazard models were used to estimate the hazard ratio for PR status. Data from a New Zealand study of 11,365 patients with early invasive breast cancer were used for external validation. Model calibration and discrimination were used to test the model performance.

RESULTS

Having a PR-positive tumour was associated with a 23% and 28% lower risk of dying from breast cancer for women with oestrogen receptor (ER)-negative and ER-positive breast cancer, respectively. The area under the ROC curve increased with the addition of PR status from 0.807 to 0.809 for patients with ER-negative tumours (p = 0.023) and from 0.898 to 0.902 for patients with ER-positive tumours (p = 2.3 × 10-6) in the New Zealand cohort. Model calibration was modest with 940 observed deaths compared to 1151 predicted.

CONCLUSION

The inclusion of the prognostic effect of PR status to PREDICT Breast has led to an improvement of model performance and more accurate absolute treatment benefit predictions for individual patients. Further studies should determine whether the baseline hazard function requires recalibration.

External Quality Assessment 2.0: The Importance of a Standardized Implementation of TILs for Daily and Trial Practices

New assays are developed regularly to improve health care for patients. It is important to ensure that assays are performed correctly. Therefore, it is advised to participate in training and proficiency (competence assessment) programs. Tumor infiltrating lymphocytes (TILs) might improve the estimates of response to therapy and prognosis. Herewith, we propose a new training and proficiency program in which each pathologist can train and test themselves regarding TILs (and PDL1) scoring.

Current and future diagnostic and treatment strategies for patients with invasive lobular breast cancer

BACKGROUND

Invasive lobular breast cancer (ILC) is the second most common type of breast cancer after invasive breast cancer of no special type (NST), representing up to 15% of all breast cancers.

DESIGN

Latest data on ILC are presented, focusing on diagnosis, molecular make-up according to the European Society for Medical Oncology Scale for Clinical Actionability of molecular Targets (ESCAT) guidelines, treatment in the early and metastatic setting and ILC-focused clinical trials.

RESULTS

At the imaging level, magnetic resonance imaging-based and novel positron emission tomography/computed tomography-based techniques can overcome the limitations of currently used imaging techniques for diagnosing ILC. At the pathology level, E-cadherin immunohistochemistry could help improving inter-pathologist agreement. The majority of patients with ILC do not seem to benefit as much from (neo-)adjuvant chemotherapy as patients with NST, although chemotherapy might be required in a subset of high-risk patients. No differences in treatment efficacy are seen for anti-human epidermal growth factor receptor 2 (HER2) therapies in the adjuvant setting and cyclin-dependent kinases 4 and 6 inhibitors in the metastatic setting. The clinical utility of the commercially available prognostic gene expression-based tests is unclear for patients with ILC. Several ESCAT alterations differ in frequency between ILC and NST. Germline BRCA1 and PALB2 alterations are less frequent in patients with ILC, while germline CDH1 (gene coding for E-cadherin) alterations are more frequent in patients with ILC. Somatic HER2 mutations are more frequent in ILC, especially in metastases (15% ILC versus 5% NST). A high tumour mutational burden, relevant for immune checkpoint inhibition, is more frequent in ILC metastases (16%) than in NST metastases (5%). Tumours with somatic inactivating CDH1 mutations may be vulnerable for treatment with ROS1 inhibitors, a concept currently investigated in early and metastatic ILC.

CONCLUSION

ILC is a unique malignancy based on its pathological and biological features leading to differences in diagnosis as well as in treatment response, resistance and targets as compared to NST.

Abstract 507: Trop-2 expression in triple-negative breast cancer according to histological subtype: correlations with tumor infiltrating lymphocytes (TILs) and survival

Background: Trop-2 is a transmembrane calcium signal transducer highly expressed in multiple solid tumors including breast cancer. Limited data exist about associations between Trop-2 protein expression, clinicopathological characteristics and outcome in triple-negative breast cancers (TNBC). Given the approval of sacituzumab govitecan in unselected TNBC, its evaluation in other breast cancer settings and the emergence of other Trop-2 targeted antibody-drug conjugates, Trop-2 emerges as an important drug target in solid tumors.

Methods: Trop-2-expression of patients with TNBC diagnosed between 2000-2017 at UZ Leuven was determined with IHC (ab227689, Abcam) (continuous and categorical variables, high 201-300, medium 100-200 and low &lt;100 H-score). Associations of Trop-2-expression with age, BMI, germline BRCA status, tumor grade and size, histological subtype, lymphovascular invasion (LVI), presence of DCIS, nodal status, stromal TILs, androgen receptor (AR), standardized mitotic index, and outcome (invasive disease-free survival (iDFS), distant recurrence-free survival (D-RFi) and breast cancer-specific survival (BCSS)) were assessed. Associations with continuous variables were assessed by the Spearman correlation coefficient (ρ). Group differences were assessed by the Kruskal Wallis test for multiple groups or Mann-Whitney U test for two groups. Cox proportional hazards models were used to assess the association between Trop-2 expression and outcome.

Results: Total of 658 patients with a median age at diagnosis of 53y (range 22-89y) were included, with median follow-up 9.6y. Low, medium and high Trop-2 expression was seen in 58.2%, 25.3% and 16.5% of cases. AR was positive in 25.5% of cases (10%-cutoff). Highest Trop-2 expression was observed in tumors with apocrine histology (median 180 score), and lowest expression in tumors with metaplastic histology (median 45 score) (p&lt;.001). Higher Trop-2 expression was correlated with higher AR expression (10%-cutoff) (p=0.009), more presence of nodal involvement (p=0.016), associated DCIS (p=0.004) and LVI (p=0.006). Trop-2 expression was not associated with pathological complete response (pCR) observed in 22 of 64 patients treated with neoadjuvant chemotherapy (p=0.96). There was an iDFS events frequency of 199 out of 658 (30.2%). There was no correlation between Trop-2 expression and sTILs or outcome.

Conclusion: In patients with TNBC in a large tertiary center, higher Trop-2 expression was correlated with apocrine histology, higher AR expression, more associated DCIS, more LVI and nodal involvement. There was no correlation between Trop-2 expression and sTILs or outcome.

Citation Format: Hava Izci, Kevin Punie, Lise Waumans, Annouschka Laenen, Hans Wildiers, Freija Verdoodt, Christine Desmedt, Jan Ardui, Ann Smeets, Sileny Han, Ines Nevelsteen, Patrick Neven, Giuseppe Floris. Trop-2 expression in triple-negative breast cancer according to histological subtype: correlations with tumor infiltrating lymphocytes (TILs) and survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 507.

Inter-observer agreement for the histological diagnosis of invasive lobular breast carcinoma

Invasive lobular breast carcinoma (ILC) is the second most common breast carcinoma (BC) subtype and is mainly driven by loss of E‐cadherin expression. Correct classification of BC as ILC is important for patient treatment. This study assessed the degree of agreement among pathologists for the diagnosis of ILC. Two sets of hormone receptor (HR)‐positive/HER2‐negative BCs were independently reviewed by participating pathologists. In set A (61 cases), participants were provided with hematoxylin/eosin (HE)‐stained sections. In set B (62 cases), participants were provided with HE‐stained sections and E‐cadherin immunohistochemistry (IHC). Tumor characteristics were balanced. Participants classified specimens as non‐lobular BC versus mixed BC versus ILC. Pairwise inter‐observer agreement and agreement with a pre‐defined reference diagnosis were determined with Cohen's kappa statistics. Subtype calls were correlated with molecular features, including CDH1/E‐cadherin mutation status. Thirty‐five pathologists completed both sets, providing 4,305 subtype calls. Pairwise inter‐observer agreement was moderate in set A (median κ = 0.58, interquartile range [IQR]: 0.48–0.66) and substantial in set B (median κ = 0.75, IQR: 0.56–0.86, p < 0.001). Agreement with the reference diagnosis was substantial in set A (median κ = 0.67, IQR: 0.57–0.75) and almost perfect in set B (median κ = 0.86, IQR: 0.73–0.93, p < 0.001). The median frequency of CDH1/E‐cadherin mutations in specimens classified as ILC was 65% in set A (IQR: 56–72%) and 73% in set B (IQR: 65–75%, p < 0.001). Cases with variable subtype calls included E‐cadherin‐positive ILCs harboring CDH1 missense mutations, and E‐cadherin‐negative ILCs with tubular elements and focal P‐cadherin expression. ILCs with trabecular growth pattern were often misclassified as non‐lobular BC in set A but not in set B. In conclusion, subtyping of BC as ILC achieves almost perfect agreement with a pre‐defined reference standard, if assessment is supported by E‐cadherin IHC. CDH1 missense mutations associated with preserved E‐cadherin protein expression, E‐ to P‐cadherin switching in ILC with tubular elements, and trabecular ILC were identified as potential sources of discordant classification.

Abstract P1-02-09: Results of a worldwide survey on the currently used histopathological diagnostic criteria for invasive lobular breast cancer (ILC)

Background. ILC represents the second most common histological type of breast cancer (BC), accounting for approximately 15% of all invasive BCs. Loss of cell-cell adhesion due to genomic alterations of CDH1,. the gene coding for E-cadherin, is the hallmark of ILC. So far, in the WHO guidelines, it is essential to recognize the dispersed or linear discohesive cells but it is not mandatory to demonstrate E-cadherin loss by immunohistochemistry (IHC) for diagnosing ILC. Recent central pathology revisions of clinical trials have demonstrated overdiagnosis of ILC in local pathological diagnosis, as only ~60% of the locally diagnosed ILCs were confirmed by central pathology. To understand the possible underlying reasons, we undertook a worldwide survey on the currently used histopathological diagnostic criteria for ILC. Materials and Methods. A survey was drafted using the online tool SurveyMonkey by a panel of pathologists and researchers from the European Lobular Breast Cancer Consortium (ELBCC). This survey was circulated to pathologists from December 14, 2020 until July, 1 2021. The main goals were to register the use of E-cadherin as a diagnostic marker for ILC and the systematic reporting of the ILC subtypes. Results. A total of 149 entries were recorded from 34 different countries from 6 continents. Pathologists declared working in a large tertiary (30%, 44/149) or university hospital (56%, 84/149), with an average yearly volume of BC samples &gt;300 in 111/149 (74%) and &gt;500 in 80/149 (54%) respondents. 117/149 (79%) are specialized in breast pathology. About half of the pathologists systematically perform IHC for ILC diagnosis (52%, 77/149), whilst others only perform staining in case of doubt (43%, 64/149) or for differentiating DCIS from LCIS (3%, 4/149). There was no association between the systematic use of IHC, the volume of BC samples, the type of institution (academic, large tertiary, private), and the number of pathologists in the institution. Concerning the use of IHC, 141/145(97%) participants use E-cadherin, 35/145 (24%) use β-catenin and 49/145 (34%) use p120-catenin. The majority (50%, 73/145) uses only E-cadherin, 13% (19/145) use E-cadherin in combination with β-catenin or 23% (33/145) use E-cadherin with p120-catenin, while 11% (16/145) use all 3 antibodies. For E-cadherin, 11 different clones were reported, of which the NCH-38 is the most frequently used (45%, 39/86), followed by Clone 36 (17%, 15/86) and EP700Y (16%, 14/86). Heterogeneity is reported regarding the used concentration per clone. The most frequently used modality of antigen retrieval is the heat induced one. Similar findings were observed for β-catenin and p120-catenin with each 4 different clones reported, again with variable concentrations. Only 4/104 (4%) respondents reported to perform DNA sequencing for CDH1 for diagnosing ILC. Most special lobular types are systematically reported by the vast majority of the pathologists: classic (149/149, 100%), pleomorphic (140/149, 94%), solid (108/149, 72%), histiocytoid/apocrine (90/149, 60%), alveolar (90/149, 60%), trabecular (54/149, 36%), mixed non-classic (54/149, 36%) and mucinous (51/149, 34%). Conclusions. We report the results of the first worldwide survey concerning diagnosis of ILC in pathological practice. The results demonstrate that ~half of the institutions systematically perform E-cadherin IHC to support the diagnosis of ILC. There is a great variability in E-cadherin antibody clones used as well as their concentrations, which might result in differences in staining results and their interpretation. As ILC-specific therapeutic avenues are currently being explored, some of which already in the context of clinical trials, it is of utmost importance to further improve the standardization of ILC diagnosis at the pathology level.

Citation Format: Maxim De Schepper, Anne Vincent-Salomon, Matthias Christgen, Karen Van Baelen, Hitoshi Tsuda, Sasagu Kurozumi, Maria Jose Brito, Gabor Cserni, Stuart Schnitt, Denis Larsimont, Janina Kulka, Pedro Luis Fernandez, Paula Rodriguez, Ana Aula, Cristina Mendelez, Mieke Van Bockstal, Aniko Kovacs, Zsuzsanna Varga, Jelle Wesseling, Rohit Bhargava, Pia Boström, Camille Franchet, Blessing Zambuko, Gustavo Matute, Anca Berghian, Paul van Diest, Steffi Oesterreich, Patrick WB Derksen, Giuseppe Floris, Christine Desmedt. Results of a worldwide survey on the currently used histopathological diagnostic criteria for invasive lobular breast cancer (ILC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-02-09.

Abstract P2-08-23: Early intratumoral changes after a single dose of anti-PD-1 treatment in patients with early breast cancer (BC)

Intro: Despite the growing success of immune checkpoint blockade in BC, the underlying mechanisms of response or resistance to these treatments is still poorly understood. We recently conducted a window-of-opportunity study (BioKey) including 54 patients with early BC (NCT03197389) in which patients were treated with one dose of pembrolizumab 10 ± 4 days before surgery. A tumor biopsy was taken before and after the administration of pembrolizumab. Using single-cell transcriptome profiling, we identified patients with clonotype expansion of PD-1-expressing T-cells after treatment with pembrolizumab (Bassez A, Vos H et al, Nature Medicine 2021). Expansion mainly involved CD8+ T - and CD4+ T cells. We designated these as patients with clonotype expansion or ‘expanders’ (E), whereas patients lacking clonotype expansion were considered ‘non-expanders’ (NE). In this study, we aimed at investigating the association between stromal tumor infiltrating lymphocytes (sTIL) and various immune markers using immunohistochemistry with the E phenotype. Methods: The BioKey trial has 2 cohorts. The first one included 39 treatment-naive patients who were scheduled for upfront surgery. The second cohort included 15 patients with an estimated residual tumor size of at least 1cm on imaging after neo-adjuvant chemotherapy. All molecular subtypes were represented: triple-negative (TN) BC (n= 18, 8 E and 10 NE), HER2-positive BC (n= 5, 1 E and 4 NE) and hormone receptor (HR)-positive/HER2-negative BC (n= 17, 3 E and 14 NE). 7 core biopsies and 5 resection slides were not contributive and were excluded. The expander status of 14 patients was unknown. sTIL were evaluated and immunohistochemical stains (CD3, CD4, CD8, CD68, CD73, FoxP3, Ki67, PD-1 and PD-L1) were performed. Associations between expander status and biomarkers were assessed using firth logistic regressions, adjusting per cohort. Biomarkers were considered as continuous variables and Odds Ratio computed per one unit increase on a non-transformed scale. Given the low number of E in cohort B, subgroup analyses were performed only in cohort A. Results: We observed that 1) higher levels of sTIL, PD-1+ sTIL and FOXP3+ cells in the pre-treatment biopsies, 2) higher levels of sTIL, PD1+ sTIL, PD-L1+, CD3+, CD4+, CD8+, CD68+, FOXP3+ cells and Ki67 in the post-treatment surgical specimen, as well as, 3) higher delta values (surgical specimen - biopsy) of sTIL, CD3+, CD4+, CD8+, CD68+ and Ki67 are associated with the E phenotype (Table 1). With regard to the subgroup analyses, we observed that higher levels of PD-1+ sTIL and CD68+ cells at diagnosis and surgery respectively, as well as higher delta values for CD68+, Ki67 and sTIL were associated with the E phenotype in HR+/HER2- BC, while high levels of FOXP3+ cells and PD-1+ sTILs in the biopsies, high levels of sTIL, CD3+, CD4+, CD8+, CD68+, FOXP3+, PD-1+ sTILs, PD-L1+ and Ki67 as well as higher delta values for PD-L1+ in the resection specimen were associated with the E phenotype in TNBC. Conclusion: We were able to detect associations between various cell populations of the tumor immune microenvironment evaluated before and after a single dose of pembrolizumab and the T-cell expansion phenotype previously defined at the single-cell level. It highlights the possible clinical utility of a biopsy taken early during treatment. Future neo-adjuvant studies will allow the validation of our findings and investigate the association between T-cell expansion and clinical outcomes.

Table 1.Association between the various biomarkers and the expanding T-cell phenotypeVariableOdds RatioLower 95% CIUpper 95% CIp-valuePre-treatment. Core biopsyCD31.071.001.160.061CD41.060.981.170.156CD81.130.951.380.161CD681.050.901.230.494CD73.tumor1.070.821.370.609CD73.on sTIL1.010.961.060.713FoxP32.251.394.030.001Ki671.021.001.050.107sTIL1.061.021.140.005PD-1 on sTIL1.731.212.830.001PD-L11.041.011.070.002Post-treatment. Resection specimenCD31.091.031.190.001CD41.151.051.29&lt;0.001CD81.581.192.34&lt;0.001CD681.471.152.15&lt;0.001CD73.tumor1.090.771.520.608CD73.on sTIL1.030.991.080.110FoxP32.051.313.82&lt;0.001Ki671.041.011.070.004sTIL1.081.031.15&lt;0.001PD-1 on sTIL1.641.152.650.004PD-L11.051.021.110.002Delta (resection-biopsy)CD31.071.011.250.029CD41.091.011.280.030CD81.211.021.690.025CD681.221.051.580.007CD73.tumor0.970.731.290.794CD73.on sTIL1.040.991.120.132FoxP31.220.891.810.219Ki671.051.001.130.031sTIL1.071.001.160.046PD-1 on sTIL0.960.701.330.765PD-L11.000.961.040.941

Citation Format: Hanne Vos, Kathleen Lambein, François Richard, Ines Nevelsteen, Ayse Bassez, Diether Lambrechts, Kevin Punie, Hans Wildiers, Giuseppe Floris, Christine Desmedt, Ann Smeets. Early intratumoral changes after a single dose of anti-PD-1 treatment in patients with early breast cancer (BC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-08-23.

Abstract P3-09-18: The association between genomic alterations and body mass index in patients with early breast cancer

Background: High body mass index (BMI) is an established risk factor for developing breast cancer (BC), especially estrogen receptor (ER)-positive, and also has been associated with adverse survival. Still, patients with BC are currently treated independently of their BMI given limited understandings of the association between BC biology and patient adiposity. In this study, using retrospective data retrieved from two large BC studies, we aimed to identify genomic alterations of primary BC that are associated with BMI in the most common histological BC subtype - invasive carcinoma of no special type (NST). Patients, Data and Methods: Clinicopathological and genomic alteration data were retrieved from two study cohorts: METABRIC (Pereira et al. 2016) and ICGC (Nik-Zainal et al. 2016), with BMI recorded at the time of diagnosis and represented as either a continuous variable or a categorical variable of three categories - lean, overweight and obese. Stratification according to ER and HER2 status resulted in two focused subgroups: NST ER+/HER2- (n=392) and NST ER-/HER2- (n=152). Mutations classified as oncogenic using a set of predefined criteria were used to determine gene-level mutation status. Copy number alteration (CNA) calls were distinguished into three event types: amplification, hemizygous deletion and homozygous deletion. We used multivariable Firth’s logistic regression models with the presence of a genomic alteration as the response variable, BMI as the predicting variable of interest, and data cohort (METABRIC vs ICGC), age group (≤50 vs &gt;50) and tumor grade (I & II vs III) as covariates, to assess the associations between BMI and recurrent gene-level genomic alterations, including gene mutations and CNAs. In a similar manner, we performed multivariable linear regression analysis, adjusting for age and tumor grade, to evaluate the associations of BMI with mutational signatures (MS) and tumor mutational burden in the ICGC NST subsets where these data are available. Results: Considering BMI as a categorical variable, we observed in the NST ER+/HER2- subgroup that PIK3CA was significantly less frequently mutated in obese compared to lean patients (33% vs 46%, odds ratio (OR) = 0.57 (95% confidence interval = (0.33, 0.97)), p = .039), while PTEN and TBX3 showed an increased frequency in overweight (6% vs 1%, OR = 4.14 (1.1, 22.34), p = .034) and obese (8% vs 1%, OR = 7.41 (1.82, 70.65), p = .008) patients, respectively. Regression analyses with BMI as a continuous variable revealed an increased prevalence of mutations in CDH1 and TBX3 genes as BMI increases by 1kg/m2 (OR = 1.14 (1.05, 1.24), p = .002, and OR = 1.13 (1.04, 1.22), p = .005, respectively) in patients with NST ER+/HER2- BC. No associations between BMI and oncogenic mutations was observed in the NST ER-/HER2- subgroup. Interrogation of gene-level CNAs in both subgroups demonstrated differences according to BMI in the prevalence of CNAs affecting a number of genes, many of which are known or have been presented with evidence to be involved in regulation of or regulated by hallmark pathways of BC, such as the MAPK/ERK, JAK/STAT and Wnt/β-catenin signaling pathways. We report a strong positive association between the single-base substitution signature 1 (SBS1), an age-correlated MS, and both continuous (coefficient (coef) = 18.3 (7.7, 28.9), p &lt; .001) and categorical BMI (obese vs lean, coef = 336.3 (187.9, 484.8), p &lt; .001) in the ICGC NST ER+/HER2- subgroup. Conclusion: This exploratory retrospective study suggests that the genomic profiles of primary BC may differ according to BMI. Clinical implications of these differences, especially the decreased prevalence of PIK3CA mutations in obese patients in the context of alpelisib, warrant further investigation. These results however indicate that patient adiposity should be taken into account in the era of personalized medicine.

Citation Format: Ha-Linh Nguyen, Tatjana Geukens, Marion Maetens, Karen Van Baelen, Maxim De Schepper, Sophia Leduc, Edoardo Isnaldi, Sam Aparicio, Ake Borg, Jane Brock, Annegien Broeks, Carlos Caldas, Andrew Green, Hazem Khout, Eyfjörð Jórunn, Stian Knappskog, Savitri Krishnamurthy, Sunil Lakhani, Anita Langerod, John WM Martens, Leigh Murphy, Serena Nik-Zainal, Colin Purdie, Emad Rakha, Andrea Richardson, Anne Salomon, Peter Simpson, Christos Sotiriou, Paul Span, Benita Kiat-Tee Tan, Alastair Thompson, Stefania Tommasi, Marc Van de Vijver, Steven Van Laere, Alain Viari, Giuseppe Floris, Elia Biganzoli, François Richard, Christine Desmedt. The association between genomic alterations and body mass index in patients with early breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-09-18.

Abstract P4-07-16: Correlation of Trop-2 expression with clinicopathological characteristics and outcome in triple-negative breast cancer (TNBC)

Purpose Trophoblast cell-surface antigen-2 (Trop-2) is a transmembrane calcium signal transducer highly expressed in multiple solid tumors including breast cancer. Trop-2 overexpression has been associated with poor survival, but limited data exist about the association between Trop-2 expression, clinicopathological characteristics and outcome in patients with TNBC. Given the approval of sacituzumab govitecan in unselected TNBC and its evaluation in other breast cancer settings, Trop-2 emerges as an important target for antibody-drug conjugates. Methods We included 470 patients with TNBC, treated with upfront surgery or upfront chemotherapy at the University Hospitals Leuven from 2000-2017. Trop-2 expression was determined with IHC (ab227689, Abcam) on whole slide tumor sections from resection specimens (upfront surgery group) or core needle-biopsy (upfront chemotherapy group) and assessed as continuous (H-score 0-300) and categorical (high 200-300, medium 100-200 and low &lt;100) variables. Stromal tumor infiltrating lymphocytes (sTIL; low, intermediate and high), mitotic score and androgen receptor (AR) expression (10%-cutoff) were scored. We assessed associations between Trop-2 expression and age, BMI (lean 18-25 (low), overweight 25-30 and obese ≥30 (high)), tumor grade and size, histological subtype, lymphovascular invasion (LVI), presence of DCIS, nodal status, sTILs, AR, standardized mitotic index and outcome (distant recurrence-free survival (DRFI), invasive disease-free survival (IDFS) and breast cancer-specific survival (BCSS)). Associations between continuous variables were assessed by the Spearman correlation coefficient (ρ). Cox proportional hazards models were used to assess the association between Trop-2 expression of tumor characteristics and outcome. Results are presented as hazard ratios (HR) with incremental increase of continuous Trop-2. Results The median age at diagnosis was 51y (range 22-85y) and the median follow-up 9.6y. For the group with upfront surgery (N=406), AR was positive in 21.5% of cases. Low, medium and high Trop-2 expression was seen in 55.7%, 23.6% and 20.7%. Higher Trop-2 expression was correlated with higher age at diagnosis (ρ=0.13, p=0.009). LVI was more frequent in Trop-2-high (39%) compared to Trop-2-medium (19%) or -low (20%) (p=0.004). Patients in Trop-2-high subgroup had more nodal involvement (45%) compared to Trop-2-medium (29%) (p=0.03). There was no correlation between Trop-2 expression with sTILs, BMI, AR or outcome. However, we found significantly improved DRFI and BCSS with increasing Trop-2 expression for the BMI-low subgroup (HR=0.95 [95%C.I. 0.89;0.99], p=0.02 and HR=0.95 [95%C.I. 0.89;0.99], p=0.04). For the group with upfront chemotherapy (N=64), AR was positive in 28.1% of cases. Low, medium and high Trop-2 expression was seen in 45.3%, 53.1% and 1.6% of cases. No difference was seen for Trop-2 expression in patients with pathological complete response (N=22) and residual disease (N=42) (median 100 vs 100 H-score, p=0.96). Higher Trop-2 expression was seen in lean compared to obese patients (100 vs 50, p=0.03). Conclusion In patients with TNBC treated with upfront surgery, higher Trop-2 expression was correlated with older age, more LVI and nodal involvement. There was overall no correlation between Trop-2 expression with sTILs, AR or outcome. Limited numbers of events warrant caution in interpretation.

Citation Format: Hava Izci, Kevin Punie, Lise Waumans, Annouschka Laenen, Hans Wildiers, Freija Verdoodt, Christine Desmedt, Jan Ardui, Ann Smeets, Sileny Han, Ines Nevelsteen, Patrick Neven, Giuseppe Floris. Correlation of Trop-2 expression with clinicopathological characteristics and outcome in triple-negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-07-16.

Common variants in breast cancer risk loci predispose to distinct tumor subtypes

BACKGROUND

Genome-wide association studies (GWAS) have identified multiple common breast cancer susceptibility variants. Many of these variants have differential associations by estrogen receptor (ER) status, but how these variants relate with other tumor features and intrinsic molecular subtypes is unclear.

METHODS

Among 106,571 invasive breast cancer cases and 95,762 controls of European ancestry with data on 173 breast cancer variants identified in previous GWAS, we used novel two-stage polytomous logistic regression models to evaluate variants in relation to multiple tumor features (ER, progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and grade) adjusting for each other, and to intrinsic-like subtypes.

RESULTS

Eighty-five of 173 variants were associated with at least one tumor feature (false discovery rate < 5%), most commonly ER and grade, followed by PR and HER2. Models for intrinsic-like subtypes found nearly all of these variants (83 of 85) associated at p < 0.05 with risk for at least one luminal-like subtype, and approximately half (41 of 85) of the variants were associated with risk of at least one non-luminal subtype, including 32 variants associated with triple-negative (TN) disease. Ten variants were associated with risk of all subtypes in different magnitude. Five variants were associated with risk of luminal A-like and TN subtypes in opposite directions.

CONCLUSION

This report demonstrates a high level of complexity in the etiology heterogeneity of breast cancer susceptibility variants and can inform investigations of subtype-specific risk prediction.

Results of a worldwide survey on the currently used histopathological diagnostic criteria for invasive lobular breast cancer

Invasive lobular carcinoma (ILC) represents the second most common subtype of breast cancer (BC), accounting for up to 15% of all invasive BC. Loss of cell adhesion due to functional inactivation of E-cadherin is the hallmark of ILC. Although the current world health organization (WHO) classification for diagnosing ILC requires the recognition of the dispersed or linear non-cohesive growth pattern, it is not mandatory to demonstrate E-cadherin loss by immunohistochemistry (IHC). Recent results of central pathology review of two large randomized clinical trials have demonstrated relative overdiagnosis of ILC, as only ~60% of the locally diagnosed ILCs were confirmed by central pathology. To understand the possible underlying reasons of this discrepancy, we undertook a worldwide survey on the current practice of diagnosing BC as ILC. A survey was drafted by a panel of pathologists and researchers from the European lobular breast cancer consortium (ELBCC) using the online tool SurveyMonkey®. Various parameters such as indications for IHC staining, IHC clones, and IHC staining procedures were questioned. Finally, systematic reporting of non-classical ILC variants were also interrogated. This survey was sent out to pathologists worldwide and circulated from December 14, 2020 until July, 1 2021. The results demonstrate that approximately half of the institutions use E-cadherin expression loss by IHC as an ancillary test to diagnose ILC and that there is a great variability in immunostaining protocols. This might cause different staining results and discordant interpretations. As ILC-specific therapeutic and diagnostic avenues are currently explored in the context of clinical trials, it is of importance to improve standardization of histopathologic diagnosis of ILC diagnosis.

Interobserver variability in the assessment of stromal tumor-infiltrating lymphocytes (sTILs) in triple-negative invasive breast carcinoma influences the association with pathological complete response: the IVITA study

High stromal tumor-infiltrating lymphocytes (sTILs) in triple-negative breast cancer (TNBC) are associated with pathological complete response (pCR) after neoadjuvant chemotherapy (NAC). Histopathological assessment of sTILs in TNBC biopsies is characterized by substantial interobserver variability, but it is unknown whether this affects its association with pCR. Here, we aimed to investigate the degree of interobserver variability in an international study, and its impact on the relationship between sTILs and pCR. Forty pathologists assessed sTILs as a percentage in digitalized biopsy slides, originating from 41 TNBC patients who were treated with NAC followed by surgery. Pathological response was quantified by the MD Anderson Residual Cancer Burden (RCB) score. Intraclass correlation coefficients (ICCs) were calculated per pathologist duo and Bland-Altman plots were constructed. The relation between sTILs and pCR or RCB class was investigated. The ICCs ranged from -0.376 to 0.947 (mean: 0.659), indicating substantial interobserver variability. Nevertheless, high sTILs scores were significantly associated with pCR for 36 participants (90%), and with RCB class for eight participants (20%). Post hoc sTILs cutoffs at 20% and 40% resulted in variable associations with pCR. The sTILs in TNBC with RCB-II and RCB-III were intermediate to those of RCB-0 and RCB-I, with lowest sTILs observed in RCB-I. However, the limited number of RCB-I cases precludes any definite conclusions due to lack of power, and this observation therefore requires further investigation. In conclusion, sTILs are a robust marker for pCR at the group level. However, if sTILs are to be used to guide the NAC scheme for individual patients, the observed interobserver variability might substantially affect the chance of obtaining a pCR. Future studies should determine the 'ideal' sTILs threshold, and attempt to fine-tune the patient selection for sTILs-based de-escalation of NAC regimens. At present, there is insufficient evidence for robust and reproducible sTILs-guided therapeutic decisions.

Papillary lesions of the breast

Papillary lesions of the breast represent a heterogeneous group of lesions including benign papillomas, papillomas with focal epithelial atypia, fully fledged ductal carcinoma in situ (DCIS) or lobular neoplasia, papillary DCIS, encapsulated papillary carcinomas without or with invasion, solid papillary carcinomas, and invasive papillary carcinomas. A micropapillary pattern characterized by lack of fibrous stalks within the papillae is observed in micropapillary DCIS and invasive micropapillary carcinoma. In addition, a variety of other rare breast lesions reveals a papillary architecture such as tall cell carcinoma with reversed polarity (TCCRP) and mucinous cystadenocarcinoma, adenomyoepithelioma, and secretory carcinoma. In addition, benign lesions such as usual ductal hyperplasia, apocrine metaplasia, gynecomastia, and juvenile papillomatosis may show a papillary or micropapillary architecture. Fragments of a benign papilloma in a breast biopsy are considered a lesion of uncertain malignant potential (B3 in the European classification) and excision is mostly recommended. Although the knowledge about molecular pathology of papillary breast lesions has increased, there is not sufficient evidence for diagnostically useful molecular features, yet. The aim of this review is to provide an update on papillary and micropapillary lesions with emphasis on problematic areas for daily diagnostic work including biopsies.