Timing of genetic testing in BRCA1/2 and PALB2-Associated breast cancer: Preoperative result disclosure increases uptake of risk-reducing mastectomy and reduces unnecessary exposure to radiotherapy

INTRODUCTION

The impact of timing of genetic testing on uptake of risk reducing mastectomy (RRM) in affected female BRCA1/2 or PALB2 carriers remains an area of evolving interest, particularly with the introduction of mainstream genetic testing initiatives.

METHODS

Women with stage I-III breast cancer and a confirmed germline pathogenic variant in BRCA1/2 or PALB2 between 2000 and 2023 were identified from an institutional genetics database. Uptake of RRM was evaluated according to disclosure of genetic testing results before or after index surgery for a first diagnosis of breast cancer.

RESULTS

The cohort included 287 female BRCA1/2 or PALB2 carriers with a median age of 44 years (IQR, 36-52). Overall, 155 (54 %) carriers received genetic testing results before and 132 (46 %) after index breast surgery. Receipt of genetic testing results before surgery was associated with a higher rate of index bilateral mastectomy (58.7 % vs. 7.6 %, p < 0.001) and a commensurate decrease in adjuvant radiation (41.9 % vs. 74.2 %, p < 0.001). At a median follow up of 4.4 years after genetic testing, 219 (76.3 %) affected carriers had undergone bilateral RRM, including 83.9 % with preoperative knowledge and 67.4 % of patients with postoperative knowledge of their germline pathogenic variant (log rank, p < 0.001). On multivariate regression, disclosure of genetic testing results before index breast surgery was independently associated with long-term uptake of bilateral mastectomy (HR 1.69, 95 % CI 1.21-2.38).

CONCLUSION

Genetic testing results delivered prior to index breast surgery increase uptake of bilateral RRM in affected BRCA1/2 and PALB2 carriers. Efforts to mainstream genetic testing would help optimize surgical decision-making.

Histology agnosticism: Infra-molecularizing disease?

The term "molecularization" has been used by historians and sociologists of science to describe the transition from an anatomic view of the body to a submicroscopic one, where health and illness, indeed life itself, are increasingly defined in terms of an individual's "genetic landscape." Here we introduce the notion of the infra-molecular as a way of extending and nuancing the molecularization trope as it applies to the domain of (post)genomic oncology. In particular we look at how infra-molecularity is enacted in practice as part of the so-called "histology-agnostic" turn in clinical cancer research and care. Drawing on fieldwork in North American oncology settings, we analyze how histology agnosticism partially reconfigures knowledge and practice across the linked domains of drug development and clinical trials, therapeutic decision making, and regulation, and the implications of this for an ongoing revision of how we understand the biopathology and temporality of cancer. We show how, in practice, the inframolecular gaze entails a "return" of histology as a modulator of histology-agnostic drugs and background for interpretation of mutational complexity.

Oncologic safety of breast conserving surgery after neoadjuvant chemotherapy in patients with multiple ipsilateral breast cancer: A retrospective multi-institutional cohort study

INTRODUCTION

The recent ACOSOG Z11102 trial demonstrated low recurrence rates with breast conserving surgery (BCS) in women with multiple ipsilateral breast cancers (MIBC). Questions remain regarding the oncologic safety of BCS in women with MIBC receiving neoadjuvant chemotherapy (NAC).

METHODS

We conducted a retrospective cohort study of adult patients who underwent BCS following NAC for stage I-III breast cancer from 2012 to 2021 at two academic centers. Descriptive statistics were used to summarize the data and the Kaplan-Meier method was used to provide estimates for recurrence and survival outcomes. MIBC was defined as ≥2 foci of malignancy.

RESULTS

A total of 544 patients were included; 29.4% (n = 160) ER+/HER2-, 17.7% (n = 96) ER+/HER2+, 18.2% (n = 99) ER-/HER2+, and 34.7% (n = 189) with ER-/HER2-disease. Overall, 80.5% (n = 438) had unifocal breast cancer while 19.5% (n = 106) had MIBC. Of patients with MIBC, 90.6% (n = 96) had multifocal and 9.4% (n = 10) had multicentric disease. Pathologic complete response was achieved in 41.1% of patients with MIBC versus 41.5% of patients with unifocal disease (p = 0.94). At a median follow-up of 55 months (IQR 32-83); 4.8% of patients in the unifocal group and 4.7% of patients in the MIBC group had had a local recurrence (p = 0.97). There was no difference in 5-year local recurrence-free survival (p = 0.92), recurrence-free survival (p = 0.06), or overall survival (p = 0.07) between the groups.

CONCLUSION

In this large cohort of women undergoing BCS post-NAC, there was no significant difference in in breast tumor recurrence or survival outcomes between patients with unifocal disease and those with MIBC.

Preoperative factors that predict pathologic nodal involvement in early-stage HER2+ breast cancer: selecting cT1cN0 patients for treatment with neoadjuvant chemotherapy versus upfront surgery

PURPOSE

The goal of this study was to identify the preoperative predictors of pathologic nodal metastases (pN+) in cT1cN0 HER2+ breast cancer undergoing upfront surgery.

METHODS

We retrospectively reviewed data from women with cT1-T2N0 HER2+ breast cancer treated with neoadjuvant therapy (NAC) or upfront surgery at our institution between 2012 and 2023. Factors associated with management strategy were evaluated, and in those undergoing upfront surgery, univariate analyses were performed to identify the clinicopathologic factors associated with nodal metastases.

RESULTS

Overall, 255 women with cT1-T2N0 HER2+ breast cancer met inclusion criteria, including 170 (68.6%) upfront surgery patients and 85 (31.4%) who underwent NAC. The median age at diagnosis was 59 years (range, 27-90 years). Younger age, larger clinical tumor size, high-grade disease, ER-PR-HER2+ subtype, and year of diagnosis after 2019 were significantly associated with receipt of NAC (p < 0.05). In those undergoing upfront surgery, 25.3% were pN+ , including 32.5% of cT1cN0 tumors. Factors associated with nodal involvement included age under 50, larger clinical tumor size, lymphovascular invasion (LVI), multifocality/multicentricity, and abnormal lymph nodes on axillary ultrasound (p < 0.05). In subset analysis of cT1cN0 HER2+ cases, LVI remained the strongest predictor of pN + disease (73.3% vs. 22.6%, p < 0.001). Patients with cT1cN0 HER2+ breast cancer under 50 years had a 47.1% likelihood of pN+ disease.

CONCLUSION

Patients with cT1cN0 breast cancer have a 32.5% likelihood of nodal metastases, with higher incidence with younger age, LVI, multifocality/multicentricity, and abnormal axillary ultrasound. The presence of these factors may identify the patients who would benefit from treatment with neoadjuvant chemotherapy.

"I just wanted more": Hereditary cancer syndromes patients' perspectives on the utility of circulating tumour DNA testing for cancer screening

Hereditary cancer syndromes (HCS) predispose individuals to a higher risk of developing multiple cancers. However, current screening strategies have limited ability to screen for all cancer risks. Circulating tumour DNA (ctDNA) detects DNA fragments shed by tumour cells in the bloodstream and can potentially detect cancers early. This study aimed to explore patients' perspectives on ctDNA's utility to help inform its clinical adoption and implementation. We conducted a qualitative interpretive description study using semi-structured phone interviews. Participants were purposively sampled adult HCS patients recruited from a Canadian HCS research consortium. Thirty HCS patients were interviewed (n = 19 women, age range 20s-70s, n = 25 were white). Participants were highly concerned about developing cancers, particularly those without reliable screening options for early detection. They "just wanted more" than their current screening strategies. Participants were enthusiastic about ctDNA's potential to be comprehensive (detect multiple cancers), predictive (detect cancers early) and tailored (lead to personalized clinical management). Participants also acknowledged ctDNA's potential limitations, including false positives/negatives risks and experiencing additional anxiety. However, they saw ctDNA's potential benefits outweighing its limitations. In conclusion, participants' belief in ctDNA's potential to improve their care overshadowed its limitations, indicating patients' support for using ctDNA in HCS care.

Awareness and Candidacy for Endocrine Prevention and Risk Reducing Mastectomy in Unaffected High-Risk Women Referred for Breast Cancer Risk Assessment

INTRODUCTION

Primary prevention of breast cancer in women at elevated risk includes several strategies such as endocrine prevention and risk-reducing mastectomy (RRM). The objective of this study was to evaluate awareness of different preventive strategies across high-risk subgroups.

PATIENTS AND METHODS

Women referred for high risk evaluation between 2020 and 2023 completed an initial risk-assessment questionnaire that included questions around perceived lifetime risk and consideration of preventive strategies. One-way analysis of variance (ANOVA) and chi-squared tests were used to compare differences across different high-risk subgroups.

RESULTS

482 women with a median age of 43 years (20-79 years) met inclusion criteria; 183 (38.0%) germline pathogenic variant carriers (GPV), 90 (18.7%) with high-risk lesions (HRL) on breast biopsy, and 209 (43.4%) with strong family history (FH) without a known genetic predisposition. Most high-risk women reported that they had considered increased screening and surveillance (83.7%) and lifestyle strategies (80.6%), while fewer patients had considered RRM (39.8%) and endocrine prevention (27.0%). Prior to initial consultation, RRM was more commonly considered in GPV carriers (59.4%) relative to those with HRL (33.3%) or strong FH (26.3%, p < 0.001). Based on current guidelines, 206 (43%) patients were deemed eligible for endocrine prevention, including 80.5% with HRL and 39.0% with strong FH. Prior consideration of endocrine prevention was highest in patients with HRL and significantly lower in those with strong FH (47.2% HRL versus 31.1% GPV versus 18.7% FH, p = 0.001).

CONCLUSIONS

Endocrine prevention is the least considered preventive option for high-risk women, despite eligibility in a significant proportion of those presenting with HRL or strong FH.

Surgical Decision Making in Genetically High-Risk Women: Quantifying Postoperative Complications and Long-Term Risks of Supplemental Surgery After Risk-Reducing Mastectomy

BACKGROUND

Risk-reducing mastectomy (RRM) helps prevent breast cancer in high-risk women but also carries a risk of unanticipated supplemental surgeries. We sought to determine the likelihood of supplemental surgeries following RRM.

METHODS

We performed a retrospective cohort study of female patients with a confirmed germline pathogenic variant (GPV) in a breast cancer susceptibility gene (BRCA1/2, PALB2 and others) who underwent bilateral or contralateral RRM at our institution between 2006 and 2022. Supplemental surgeries were defined as any operation requiring general or local anesthesia performed outside of the initially planned procedure(s). The Kaplan-Meier method was used to estimate the 5-years cumulative incidence of supplemental surgery.

RESULTS

Of 560 GPV carriers, RRMs were performed in 258 (46.1%) women. The median age of the cohort was 44 years (interquartile range 37-52 years), with 33 (12.8%) patients undergoing RRM without reconstruction and 225 (87.2%) undergoing RRM with reconstruction. Following surgery, 34 patients (13.2%) developed early (< 30 days) postoperative complications, including infection, hematoma, seroma, loss of the nipple areola complex, flap necrosis, implant exposure and/or prosthesis removal. At a median follow-up of 3.8 years, 94 (36.4%) GPV carriers underwent at least one reoperation. Participants who experienced an early postoperative complication had the highest rate of reoperation (85.3% vs. 29.0%; p < 0.001) and a significantly higher likelihood of multiple additional surgical interventions (41.2% vs. 10.7%; p < 0.001). The 5-years rate of supplemental surgery was 39.2% [95% confidence interval (CI) 32.7-46.5] in the overall cohort and 31.5% (95% CI 24.9-39.3) in patients without an early postoperative complication.

CONCLUSIONS

Unanticipated supplemental surgeries occur in 40% of GPV carriers following RRM and in nearly one-third of patients without early postoperative complications.

The Mutational Spectrum of Pre- and Post-Neoadjuvant Chemotherapy Triple-Negative Breast Cancers

The response of triple-negative breast cancer (TNBC) patients to pre-operative (neoadjuvant chemotherapy) is a critical factor of their outcome. To determine the effects of chemotherapy on the tumor genome and to identify mutations associated with chemoresistance and sensitivity, we performed whole exome sequencing on pre/post-chemotherapy tumors and matched lymphocytes from 26 patients. We observed great inter-tumoral heterogeneity with no gene mutated recurrently in more than four tumors besides TP53. Although the degree of response to chemotherapy in residual tumors was associated with more subclonal changes during chemotherapy, there was minimal evolution between pre/post-tumors. Indeed, gene sets enriched for mutations in pre- and post-chemotherapy tumors were very similar and reflected genes involved in the biological process of neurogenesis. Somatically mutated genes present in chemosensitive tumors included COL1A2, PRMD15, APOBEC3B, PALB2 and histone protein encoding genes, while BRCA1, ATR, ARID1A, XRCC3 and genes encoding for tubulin-associated proteins were present in the chemoresistant tumors. We also found that the mutational spectrum of post-chemotherapy tumors was more reflective of matching metastatic tumor biopsies than pre-chemotherapy samples. These findings support a portrait of modest ongoing genomic instability with respect to single-nucleotide variants induced by or selected for by chemotherapy in TNBCs.

A micro-flow, high-pH, reversed-phase peptide fractionation and collection system for targeted and in-depth proteomics of low-abundance proteins in limiting samples

We present a method and a simple system for high-pH RP-LC peptide fractionation of small sample amounts (30-60 µg), at micro-flow rates with micro-liter fraction collection using ammonium bicarbonate as an optimized buffer for system stability and robustness. The method is applicable to targeted mass spectrometry approaches and to in-depth proteomic studies where the amount of sample is limited. Using targeted proteomics with peptide standards, we present the method's analytical parameters, and potential in increasing the detection of low-abundance proteins that are difficult to quantify with direct targeted or global LC-MS analyses. This fractionation system increased peptide signals by up to 18-fold, while maintaining high quantitative precision, with high fractionation reproducibility across varied sample sets. In real applications, it increased the detection of targeted endogenous peptides by two-fold in a 25 cell-cycle-control protein panel, and in-depth MS analyses of nuclear extracts, it allowed the detection of up to 8,896 proteins with 138,417 peptides in 24-concatenated fractions compared to 3,344 proteins with 23,093 peptides without fractionation. In a relevant biological problem of CDK4/6-inhibitors and breast cancer, the method reproduced known information and revealed novel insights, highlighting that it can be successfully applied in studies involving low-abundance proteins and limited samples. •Tested nine high-pH buffer/solvent systems to obtain a robust, effective, and reproducible micro-flow fractionation method which was devoid of commonly encountered LC clogging/pressure issues after months of use.•Peptide enrichment method to improve detection and quantitation of low-abundance proteins in targeted and in-depth proteomic studies.•Can be applied to diverse protein samples where the available amount is limited.

Current and new frontiers in hereditary cancer surveillance: Opportunities for liquid biopsy

At least 5% of cancer diagnoses are attributed to a causal pathogenic or likely pathogenic germline genetic variant (hereditary cancer syndrome-HCS). These individuals are burdened with lifelong surveillance monitoring organs for a wide spectrum of cancers. This is associated with substantial uncertainty and anxiety in the time between screening tests and while the individuals are awaiting results. Cell-free DNA (cfDNA) sequencing has recently shown potential as a non-invasive strategy for monitoring cancer. There is an opportunity for high-yield cancer early detection in HCS. To assess clinical validity of cfDNA in individuals with HCS, representatives from eight genetics centers from across Canada founded the CHARM (cfDNA in Hereditary and High-Risk Malignancies) Consortium in 2017. In this perspective, we discuss operationalization of this consortium and early data emerging from the most common and well-characterized HCSs: hereditary breast and ovarian cancer, Lynch syndrome, Li-Fraumeni syndrome, and Neurofibromatosis type 1. We identify opportunities for the incorporation of cfDNA sequencing into surveillance protocols; these opportunities are backed by examples of earlier cancer detection efficacy in HCSs from the CHARM Consortium. We seek to establish a paradigm shift in early cancer surveillance in individuals with HCSs, away from highly centralized, regimented medical screening visits and toward more accessible, frequent, and proactive care for these high-risk individuals.

Predictors of nodal metastases in early stage HER2+ breast cancer: Deciding on treatment approach with neoadjuvant chemotherapy vs. upfront surgery

BACKGROUND

The purpose of this study is to evaluate preoperative predictors of nodal metastases in patients with early-stage, HER2-positive (HER2+) breast cancer.

METHODS

The SEER Database was queried to identify women with a first diagnosis of stage I-II (T1-T2) HER2-positive breast cancer treated with upfront surgery in 2018. Multivariable logistic regression was used to identify clinical characteristics independently associated with nodal involvement.

RESULTS

Overall, 3333 women with stage I-II HER2+ breast cancer met inclusion criteria and were included in the study. The median age at diagnosis was 59 years (IQR, 51-69 years). Most patients underwent breast-conserving surgery (60.9%), with a median of 3 (IQR 2-4) axillary lymph nodes removed. On final pathology, 762 (22.9%) of T1-T2 HER2+ patients were node positive; 2.7% pN0[i+], 3.7% pN1mi, 15.1% pN1, and 1.4% pN2. Women less than 40 years and those between 40 and 49 years showed the highest proportion of axillary lymph node metastasis, in 33.7% and 30.7% respectively, and declining with age (p < 0.001). Patients with triple-positive breast cancer had the highest rates of nodal involvement (24.8%), compared to 20.7% ER+/PR-/HER2+ and 19.6% of HER2-enriched patients (p = 0.006). On adjusted analysis, age, biologic subtype, tumour size, and type of surgery remained independent predictors of nodal involvement. On subgroup analysis, women under age 50 with T1c HER2-enriched or triple-positive breast cancer had a 33% and 35% incidence of nodal involvement, which declined with age.

CONCLUSIONS

The likelihood of pathologic nodal involvement in early-stage HER2+ breast cancer is contingent on age, ER/PR status, and tumour size.

Retrospective study to estimate the prevalence and describe the clinicopathological characteristics, treatments received, and outcomes of HER2-low breast cancer

BACKGROUND

Approximately 80% of all breast cancers (BCs) are currently categorized as human epidermal growth factor receptor 2 (HER2)-negative [immunohistochemistry (IHC) 0, 1+, or 2+/in situ hybridization (ISH) negative]; approximately 60% of BCs traditionally categorized as HER2-negative express low levels of HER2. HER2-low (IHC 1+ or IHC 2+/ISH-) status became clinically actionable with approval of trastuzumab deruxtecan to treat unresectable/metastatic HER2-low BC. Greater understanding of patients with HER2-low disease is urgently needed.

PATIENTS AND METHODS

This global, multicenter, retrospective study (NCT04807595) included tissue samples from patients with confirmed HER2-negative unresectable/metastatic BC [any hormone receptor (HR) status] diagnosed from 2014 to 2017. Pathologists rescored HER2 IHC-stained slides as HER2-low (IHC 1+ or IHC 2+/ISH-) or HER2 IHC 0 after training on low-end expression scoring using Ventana 4B5 and other assays at local laboratories (13 sites; 10 countries) blinded to historical scores. HER2-low prevalence and concordance between historical scores and rescores were assessed. Demographics, clinicopathological characteristics, treatments, and outcomes were examined.

RESULTS

In rescored samples from 789 patients with HER2-negative unresectable/metastatic BC, the overall HER2-low prevalence was 67.2% (HR positive, 71.1%; HR negative, 52.8%). Concordance was moderate between historical and rescored HER2 statuses (81.3%; κ = 0.583); positive agreement was numerically higher for HER2-low (87.5%) than HER2 IHC 0 (69.9%). More than 30% of historical IHC 0 cases were rescored as HER2-low overall (all assays) and using Ventana 4B5. There were no notable differences between HER2-low and HER2 IHC 0 in patient characteristics, treatments received, or clinical outcomes.

CONCLUSIONS

Approximately two-thirds of patients with historically HER2-negative unresectable/metastatic BC may benefit from HER2-low-directed treatments. Our data suggest that HER2 reassessment in patients with historical IHC 0 scores may be considered to help optimize selection of patients for treatment. Further, accurate identification of patients with HER2-low BC may be achieved with standardized pathologist training.

Evaluation of a 'plug and play' nanoflow liquid chromatography system for MS-based proteomic characterization of clinical FFPE specimens

INTRODUCTION

Proteomic analysis of formalin-fixed paraffin-embedded (FFPE) tumor tissue specimens has gained interest in the last 5 years due to technological advances and improved sample collection, as well as biobanking for clinical trials. The real-world implementation of clinical proteomics to these specimens, however, is hampered by tedious sample preparation steps and long instrument acquisition times.

AREAS COVERED

To advance the translation of quantitative proteomics into the clinic, we are comparing the performance of the leading commercial nanoflow liquid chromatography (nLC) system (based on literature reviews), the Easy-nLC 1200 (Thermo Fisher Scientific, Waltham, MA, U.S.A.), to the Evosep One HPLC (Evosep Biosystems, Odense, Denmark). We measured FFPE-tissue digests from 21 biological replicates with a similar gradient on both of the LC systems while keeping the on-column amount (1 µg total protein) and the single-shot data-dependent acquisition-based MS/MS method constant.

EXPERT OPINION

Overall, the Evosep One facilitates robust and sensitive high-throughput sample acquisition, making it suitable for clinical MS. We found the Evosep One to be a useful platform for positioning mass spectrometry-based proteomics in the clinical setting. The clinical application of nLC/MS will inform clinical decision-making in oncology and other diseases.

Biomarker Data from the Phase III KATHERINE Study of Adjuvant T-DM1 versus Trastuzumab for Residual Invasive Disease after Neoadjuvant Therapy for HER2-Positive Breast Cancer

PURPOSE

In KATHERINE, adjuvant T-DM1 reduced risk of disease recurrence or death by 50% compared with trastuzumab in patients with residual invasive breast cancer after neoadjuvant therapy (NAT) comprised of HER2-targeted therapy and chemotherapy. This analysis aimed to identify biomarkers of response and differences in biomarker expression before and after NAT.

EXPERIMENTAL DESIGN

Exploratory analyses investigated the relationship between invasive disease-free survival (IDFS) and HER2 protein expression/gene amplification, PIK3CA hotspot mutations, and gene expression of HER2, PD-L1, CD8, predefined immune signatures, and Prediction Analysis of Microarray 50 intrinsic molecular subtypes, classified by Absolute Intrinsic Molecular Subtyping. HER2 expression on paired pre- and post-NAT samples was examined.

RESULTS

T-DM1 appeared to improve IDFS versus trastuzumab across most biomarker subgroups, except the HER2 focal expression subgroup. High versus low HER2 gene expression in residual disease was associated with worse outcomes with trastuzumab [HR, 2.02; 95% confidence interval (CI), 1.32-3.11], but IDFS with T-DM1 was independent of HER2 expression level (HR, 1.01; 95% CI, 0.56-1.83). Low PD-L1 gene expression in residual disease was associated with worse outcomes with trastuzumab (HR, 0.66; 95% CI, 0.44-1.00), but not T-DM1 (HR, 1.05; 95% CI, 0.59-1.87). PIK3CA mutations were not prognostic. Increased variability in HER2 expression was observed in post-NAT versus paired pre-NAT samples.

CONCLUSIONS

T-DM1 appears to overcome HER2 resistance. T-DM1 benefit does not appear dependent on immune activation, but these results do not rule out an influence of the tumor immune microenvironment on the degree of response.

Abstract HER2-15: HER2-15 Retrospective Study to Estimate the Prevalence and Describe the Clinicopathological Characteristics, Treatment Patterns, and Outcomes of HER2-Low Breast Cancer

Background: About 60% of breast cancers (BCs) traditionally categorized as HER2 negative (HER2-neg; immunohistochemistry [IHC] 0, IHC 1+ or IHC 2+/in situ hybridization [ISH]–) express low levels of HER2 (HER2-low; IHC 1+ or IHC 2+/ISH–; Schettini, NPJ Breast Cancer 2021). In the phase 3 DESTINY-Breast04 trial (NCT03734029), trastuzumab deruxtecan (T-DXd) showed significantly longer progression-free survival and overall survival (OS) vs physician’s choice of chemotherapy in patients (pts) with HER2-low metastatic BC (mBC) who previously received chemotherapy (Modi, NEJM 2022). As HER2-low becomes a clinically relevant HER2 status among pts with BC, greater understanding of pts with HER2-low disease is needed, including identification of these pts using conventional IHC assays. Our objectives were to assess the prevalence of HER2-low among HER2-neg mBC based on rescored HER2 IHC slides, to describe characteristics of pts with HER2-low mBC, and to characterize concordance between historical HER2 scores and rescores. Methods: This global, multicenter, retrospective study (NCT04807595) included pts with confirmed HER2-neg (HER2 IHC 0, 1+, or 2+/ISH−) unresectable/mBC diagnosed from 2014 through 2017. HER2 IHC-stained slides were rescored after training on low-end expression scoring using Ventana 4B5 and other assays by local laboratories at 13 sites in 10 countries blinded to historical HER2 scores. BCs were categorized as HER2-low (IHC 1+ or IHC 2+/ISH−) or HER2 IHC 0 (IHC 0 or &gt;0&lt; 1+). Prevalence of HER2-low and concordance between historical HER2 scores and rescores were assessed. Demographics, clinicopathological characteristics, treatment patterns, and outcomes were examined via data from medical charts/health records. Results: HER2 rescores were obtained for 781 pts with HER2-neg mBC. HER2-low prevalence was 67.1% overall; 71.1% in hormone receptor (HR)–positive (HR+) and 52.5% in HR–negative (HR−) subgroups. There were no notable differences in characteristics (Table) or treatment patterns between pts with HER2-low and HER2 IHC 0. The most frequent therapies used in the first treatment in the metastatic setting were endocrine therapy (64.1%) for pts with HR+ mBC and chemotherapy (94.4%) for pts with HR− mBC. Among pts with HR+ mBC, 10.2% received cyclin-dependent kinase 4/6 inhibitors as part of their first treatment. There were no statistically significant differences in clinical outcomes between the HER2-low and HER2 IHC 0 groups within each HR subgroup. For pts with HR+ mBC, median time to first subsequent treatment was 10 and 8 months for the HER2-low and HER2 IHC 0 groups, respectively. Overall, concordance was 81.2% (kappa=0.582). Concordance between historical HER2 scores and rescores was 87.3% for HER2-low and 70.1% for HER2 IHC 0 samples. Conclusions: The prevalence of HER2-low (67.1%) among pts previously categorized as HER2-neg mBC in this study was similar to that of an earlier study (≈60%). No obvious differences in patient characteristics or clinical presentation were seen between pts with HER2-low and HER2 IHC 0 mBC. Overall percentage agreement between rescored and historical HER2 scores was 81.2%; agreement was numerically greater for HER2-low than HER2 IHC 0. As HER2-targeted therapies such as T-DXd for the treatment of pts with HER2-low BC are emerging, a greater understanding of pts with HER2-low expression who may benefit from these therapies is important.

Citation Format: Giuseppe Viale, Mark Basik, Naoki Niikura, Eriko Tokunaga, Sara Brucker, Frédérique Penault-Llorca, Naoki Hayashi, Joo Hyuk Sohn, Rita Teixeira de Sousa, Adam M. Brufsky, Ciara S. O’Brien, Fernando Schmitt, Gavin Higgins, Della Varghese, Gareth D. James, Akira Moh, Andrew Livingston, Victoria de Giorgio-Miller. HER2-15 Retrospective Study to Estimate the Prevalence and Describe the Clinicopathological Characteristics, Treatment Patterns, and Outcomes of HER2-Low 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 HER2-15.

Abstract P3-08-09: Development and molecular characterization of hard-to-treat breast cancer pre-clinical models to enhance precision medicine

Invasive breast carcinoma is a combination of heterogeneous diseases with distinct molecular and clinical features. Some subsets of breast cancer present major clinical challenges, including triple-negative, metastatic/recurrent disease and rare breast histologies. Previously, we developed a unique resource of 37 hard-to-treat breast cancer patient-derived xenografts (PDX). This set included mainly triple negative breast cancer (TNBC) patients that presented poor response to neoadjuvant chemotherapies (Savage et al. 2020 - PMID: 32546838). PDXs accurately reproduce the molecular heterogeneity of the primary tumors and show that multi-drug chemoresistance was retained upon xenotransplantation. Here, we present the characterization of PDX 3-dimensional cultures organoids (8) and PDX derived epithelial cell lines (11). Using single-cell RNAseq we showed that an organoid cultured for several passages (P8) maintained the heterogeneity of the matched PDX. Although in different proportions, all cancer cell populations found in the PDX were retained in matched organoids supporting that organoids are suitable models that recapitulates the tumor heterogeneity and are therefore a suitable model for drug screening. Among our new PDXs models (30), we have developed four PDXs from rare metaplastic breast cancers (MpBC), an aggressive subtype of breast cancer that present the poorest response to standard of care chemotherapy. We also developed one male breast cancer PDX with matched organoid. Omic analysis on our pre-clinical models and patient primary tumor and metastasis will inform development of therapeutic opportunities. This molecular information will guide selection of compounds that will be validated using our high throughput organoid drug screening pipeline. This will allow rapid screens of thousands of approved drugs, enhancing drug repurposing with potential for rapid clinical translation. The combined use of 3D tumor organoids and PDXs, is an important opportunity poised to transform identification of new therapeutic options for hard-to-treat lethal breast cancers.

Citation Format: Hellen Kuasne, Anne-Marie fortier, Sandrine Busque, Simon Mathien, Paul Savage, Constanza Martinez Ramirez, Anie Monast, Margarita Soleinova, Atilla Omeroglu, Jamil Asselah, Nathaniel Bouganim, Sarkis Meterissian, Mark Basik, Morag Park. Development and molecular characterization of hard-to-treat breast cancer pre-clinical models to enhance precision medicine [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 P3-08-09.

Abstract P2-11-26: The prognostic role of circulating tumor DNA after neoadjuvant chemotherapy in triple negative breast cancer with residual tumor

Background The presence of residual tumour at surgery (non-pathological complete response or non-pCR) occurs in about half of TNBCs treated with neoadjuvant chemotherapy (NAC) and signals chemoresistance and poor prognosis. Although further adjuvant chemotherapy (Capecitabine/Xeloda) results in improved survival in patients with non-pCR, only about 15% of such patients do benefit. Circulating tumor DNA (ctDNA) is a plasma-based biomarker that can be used to reveal real-time data about the disease and treatment progression. We have previously shown that detection of ctDNA after NAC signals poor prognosis. To validate and extend our previous results using an academic hospital-based tumor bespoke assay, we performed ctDNA measurements in non-pCR TNBC patients at the pre-operative, post-operative, 3 and 6-month time points. Methods Whole exome sequencing (WES) was performed on residual tumors from 34 TNBC patients to identify tumour-specific mutations (5/patient). Digital droplet PCR (ddPCR) assays were developed for these mutations and performed as per our previous work. Patients with at least one detectable mutation were considered ctDNA positive for a given time point. The detection of ctDNA was correlated with relapse-free survival (RFS). Results The overall RFS was 44%, with 56 % of patients received adjuvant Xeloda. Detection of ctDNA at the end of NAC (T1) correlated with poor prognosis of RFS (n = 33, p-value = 0.009, HR = 0.29 (95% CI = 0.12 to 0.74)). Detection of ctDNA after surgery (T2) and while on Xeloda (T3) showed no significant prognostic value for RFS. However, ctDNA detection at the 6-month time point, after Xeloda treatment (T4), showed stronger prognostic value for RFS (n = 17, p-value = 0.004, HR = 0.12 (95% CI = 0.03 to 0.51)). When measuring changes in ctDNA detectability from T1 to T4, 4 patients initially positive became ctDNA negative after the 6-month interval, and only 1 of these 4 had a relapse, compared with 10 of 11 that remained positive at the 6-month time point (p = 0.01, Chi-squared test). 3 of the 4 patients that cleared their ctDNA had received Xeloda. In addition, 2 patients initially negative became ctDNA positive at the 6-month time point (T4) and both relapsed, compared with only 1 of 5 that remained negative at 6 months (p = 0.035, Chi-squared test). For patients who received adjuvant Xeloda ctDNA positivity at T1 was associated with a worse RFS (p-value = 0.028, HR = 3.3884 (95% CI = 1.160 to 13.00)). Conclusion ctDNA testing using ddPCR in an academic hospital-based context at the post-NAC time point as well as at 6 months after surgery identifies an excellent prognostic group in TNBC patients with non-pCR and changes in ctDNA during the adjuvant period have prognostic value. This personalized approach to treatment management is ready for prospective testing in patients who have undergone NAC and require additional chemotherapy.

Citation Format: Talia Roseshter, Anna Klemantovich, Luca Cavallone, Adriana Aguilar-Mahecha, Josiane Lafleur, Oluwadara O. Elebute, Sarah Jenna, Jean-Francois Boileau, Manuela Pelmus, Mark Basik, Cathy Lan. The prognostic role of circulating tumor DNA after neoadjuvant chemotherapy in triple negative breast cancer with residual tumor [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 P2-11-26.

Margin Status and Local Recurrence in Phyllodes Tumours of the Breast: A Canadian Series

BACKGROUND

Phyllodes tumours of the breast are rare fibroepithelial neoplasms with a propensity for recurrence. While surgical excision remains the standard of care, the optimal margin width is an area of active investigation. Recent studies have questioned the necessity for wide, local excision.

METHODS

We conducted a retrospective, cohort study of patients with phyllodes tumours treated at our institution between 2003 and 2021. Demographic, histopathological, and recurrence data were captured; malignant phyllodes were excluded. Cox proportional hazard models were used to identify covariates associated with local recurrence.

RESULTS

Of 187 patients with phyllodes tumours, 82.9% (n = 155) were classified as benign while 17.1% (n = 32) were borderline. Initial surgical margins were positive in 26.2% (n = 49), < 2 mm in 50.8% (n = 95), and ≥ 2 mm in 23% (n = 43) patients. Among patients with positive margins, 61.2% (n = 30) underwent margin revision. At a median follow-up of 2.9 years, the recurrence rate was 3.7%. On univariate analysis, only a positive margin at the time of initial surgery and not margin width was significantly associated with a higher rate of disease recurrence (hazard ratio [HR] 9.52, 95% confidence interval [CI] 1.85-49.2), as was a size greater than 4 cm on preoperative imaging (HR 10.78, 95% CI 0.97-120.1). Revision of an initially positive margin was not significantly associated with decreased local recurrence (p = 1).

CONCLUSIONS

In this large cohort of benign and borderline phyllodes tumours, positive resection margins and not margin width at the initial surgery were associated with a increased recurrence. Individualization of decisions regarding margin reexcision is important.

Abstract A033: Identification of gemcitabine-resistant populations using scRNA-sequencing in triple negative breast cancer patient-derived xenograft

Despite major advances in the treatment of breast cancer (BC), it remains the most diagnosed and second most deadly cancer among American women. BC is a heterogeneous disease consisting of distinct subtypes, including hormone receptor-positive, HER2 receptor-positive and cancers that lack these receptors categorized as triple-negative breast cancers (TNBC). The TNBC subtype presents the worst outcome and the highest rates of recurrence and metastasis. The absence of targets prevents the use of established precision therapies in TNBC, and the standard of care remains neoadjuvant chemotherapy. While this is effective in some patients, about 50% develop resistance, leading to the development of metastasis. It is known that selective pressures exerted by chemotherapy treatment can promote the outgrowth of resistant tumor subclones. However, the diverse intra-tumoral population and the mechanisms that lead to chemotherapy resistance in TNBC are still poorly understood. We hypothesized that therapeutic regimens influence tumor plasticity by exerting selective pressures leading to the outgrowth of resistant subpopulations with the greatest survival advantage. To evaluate this hypothesis, we aimed to generate in vivo models of chemotherapy resistance and to investigate the plasticity of tumor cell subpopulations challenged with standard-of-care chemotherapies. To this end, we selected a multi-drug resistant (Doxorubicin, Cyclophosphamide, Cisplatin, and Paclitaxel) BC patient and developed a patient-derived xenograft (PDX) from the primary tumor and the lung metastasis. The metastasis PDX model was initially responsive to Gemcitabine (as observed in the BC patient) but eventually developed resistance. We challenged this metastasis PDX with several cycles of Gemcitabine and obtained residual, rebound, and resistant tumor samples. We performed single-cell RNA sequencing (scRNAseq) of these models using a droplet-based technology from 10X Genomics. This scRNAseq data was used to compare the changes in the proportions of cellular subpopulations in each model. Interestingly, our data shows that the rebound model presents greater similarity to the untreated metastasis, while the resistant model has significant differences in cell population expression profiles. We identified a hypoxic population in the primary tumor and its matched metastasis. This population was validated in these models by Nanostring GeoMx Digital Spatial Profiler. Our recent analyses have identified that this hypoxic population persists in the residual, rebound and resistant models. In addition, we have identified other populations that vary in these models. We are currently investigating their cellular mechanisms and gene expression patterns. Using scRNA-sequencing to understand the clonal expansion of resistant subpopulations following chemotherapy reveals distinctive resistant cell features enabling the identification of the vulnerabilities of these tumors.

Citation Format: Sandrine Busque, Constanza Martinez Ramirez, Hellen Kuasne, Paul Savage, Anne-Marie Fortier, Anie Monast, Atilla Omeroglu, Jamil Asselah, Nathaniel Bouganim, Sarkis Meterissian, Claudia Kleinman, Mark Basik, Morag Park. Identification of gemcitabine-resistant populations using scRNA-sequencing in triple negative breast cancer patient-derived xenograft [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr A033.

Abstract 4011: Prognostic value of transcriptomic analysis in residual post neo-adjuvant triple negative breast cancer tumors

Background: Triple negative breast cancer is the most aggressive type of breast cancer. Approximately 50% of TNBC patients respond to pre-operative neo-adjuvant chemotherapy (NAC), however those patients with residual disease (non-pathological complete response or non-pCR) have a very poor prognosis. Recently, the use of capecitabine in the adjuvant setting was shown to increase disease-free survival in non-pCR patients. However, there are no biomarkers to identify patients who may benefit from adjuvant capecitabine. Moreover, novel therapeutic targets are needed to treat patients with non-pCR.

Methods: RNA extracted from 32 Formalin Fixed Paraffin Embedded (FFPE) residual post-NAC tumor samples underwent NanoString nCounter gene expression analysis using the BC360 panel as well as RNAseq.

Results: Comparison of tumors from poor (RFS&lt;2 yrs) and good prognosis (RFS&gt;2 yrs) patients showed 65 genes differentially expressed (≥1.5 fold change and p&lt;0.05) by nCounter. 40 of these genes had differential expression also validated by RNAseq (R2= 0.96) and were selected for further pathway analysis. Gene Set Enrichment Analysis (GSEA) showed an enrichment for biological pathways involved in cell cycle, with all genes in this set upregulated in the poor prognosis group. GSEA analysis of 310 upregulated genes identified by RNAseq showed an enrichment for biological pathways associated with cell population proliferation and skin development. Interestingly, one of the upregulated genes identified was TYMS, encoding thymidylate synthase, the target of capecitabine, which showed 2-fold increased expression in the poor prognosis group (p≤0.005).

Conclusion: Our results suggest that residual tumors from TNBC patients who relapse within two years of surgery show transcriptomic evidence of increased proliferation and that expression levels of TYMS may be a potential biomarker to select patients for capecitabine in the adjuvant setting.

Citation Format: Adriana Aguilar-Mahecha, Yasamin Majedi, Oluwadara Elebute, Josiane Lafleur, Andreas Papadakis, Cathy Lan, Manuela Pelmus, Touhidur Rashid, Sarah Jenna, Mark Basik. Prognostic value of transcriptomic analysis in residual post neo-adjuvant triple negative breast cancer tumors [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 4011.

Abstract 1794: The combination of Talazoparib with anti-her2 drugs shows efficacy in drug resistant Her2+ and low Her2 PDX models

Background: Her2+ breast cancer accounts for 15% of breast cancer cases and is primarily treated with a combination of Her2-targeted agents and chemotherapy. While use of targeted agents has substantially improved survival of these patients, clinical drug resistance is prevalent. DNA repair defects are a feature of cancer that has been exploited by targeted agents such as inhibitors of poly-ADP ribose polymerase (PARP). PARP inhibitors have been shown to be effective in patients with germline mutations in other DNA repair factors such as BRCA1/2. There is limited data for the use of PARP inhibitors in HER2+ breast cancers, and in tumors without BRCA1/2 mutations. Using a collection of HER2+ and HER2-low expressing breast cancer patient-derived xenografts (PDXs) that have differential responses to the Her2-targeted agents Trastuzumab, Pertuzumab, and T-DM1, we tested the combination of these agents with Talazoparib (Talzenna™), a clinically approved Parp inhibitor.

Methods: Orthotopically engrafted PDX mouse models resistant to either Trastuzumab or T-DM1 were randomized into treatment arms including Trastuzumab or T-DM1 in combination with Talazoparib, and the single agents alone. Mice are monitored for body weight and change in tumour volume every 2-3 days, then sacrificed at endpoint for survival analysis. We have also generated PDX-derived cells (PDCs) from one model with which to validate in vivo results and perform mechanistic studies. All models are being characterized for copy number changes, somatic mutations, and protein expression by immunohistochemistry.

Results: The combination of Talazoparib and either Trastuzumab or T-DM1 was effective in 3 PDX models, including a Trastuzumab-resistant HER2+ PDX, a T-DM1-resistant HER2+ PDX and a T-DM1-resistant HER2-low expressing PDX. The combinations resulted in significant delays in tumour growth (p&lt;0.05), including a transient tumour regression with the combination T-DM1+Talazoparib in 1 PDX. Median overall survival time was improved with the combination of Trastuzumab +Talazoparib (p&lt;0.05), while the combinations of T-DM1+Talazoparib increased survival time although not significantly. Notably all models have maintained Her2 expression through treatment.

Conclusion: Our results suggest that combining HER-targeted agents with Talazoparib may benefit patients with advanced HER2-therapy resistant HER2+ and low HER2+ breast cancers. Exploratory biomarker analysis and mechanistic studies using PDCs are currently underway in our laboratory.

Citation Format: Kathryn Bozek, Marguerite Buchanan, Cathy Lan, Josiane Lafleur, Cedric Darini, Urszula Krzemien, Adriana Aguilar-Mahecha, Mark Basik. The combination of Talazoparib with anti-her2 drugs shows efficacy in drug resistant Her2+ and low Her2 PDX models [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 1794.

Abstract 538: Cell-free whole genome sequencing for the detection of cancer in patients with germline BRCA1/2 mutations

Background: Hereditary breast and ovarian cancer syndrome (HBOC) is caused by a germline likely/pathogenic variant in BRCA1 or BRCA2, leading to increased risk of developing breast, ovarian, prostate, and pancreatic cancers. While HBOC patients often undergo regular surveillance including breast imaging, other cancers have no effective screening or biomarkers. One emerging technology is the analysis of circulating tumor DNA (ctDNA), fragments of DNA that are shed from the tumor into the bloodstream. In sporadic cancer, several studies have demonstrated the advantages and sensitivity of cell-free whole genome sequencing (cfWGS) compared to targeted panel sequencing. However, the use of cfWGS for cancer detection in HBOC has not been explored.

Methods: Matched tumor, germline, and plasma were collected from 5 HBOC patients (3 breast, 2 ovarian) as part of the Canada-wide CHARM consortium (https://charmconsortium.ca). Tumor (40x), germline (20x), and plasma (20x) underwent whole genome sequencing (WGS) and subsequent variant calling pipeline using an ensemble of 6 variant callers. Insertions, deletions, and structural variants were not included in downstream analyses. Plasma tumor fraction prediction and copy number alterations were performed using ichorCNA. Detection of tumor associated mutations in plasma was compared to MRDetect software.

Results: Variant calling identified an average of 11,170 tumor (7,649-16,706) and 1,215 (544-3,205) plasma SNVs per patient. Somatic BRCA1/2 mutations were detected in 0/5; whereas deletion of the intact BRCA1/2 allele was identified in 5/5 patients. An average of 24.6% (8.3%-75.9%) of plasma mutations where shared with SNVs identified in matched tumor. Targeted panel deep-sequencing (20,000X) was only able to detect mutations in TP53 in 3/5 cases (0.8% - 8.6%). Plasma derived copy number alterations correlated well with tumor derived copy number alterations in 3/5 cases and ichorCNA predicted tumor fractions ranged from 0.038 to 0.196.

Conclusions: Traditionally, targeted panel sequencing has been used to identify tumor associated mutations in plasma. While this technique is sensitive, major disadvantages include the narrow breadth of the captured regions and the inability to detect deletion events such as those that occur in BRCA1/2. Here we show that plasma WGS is effective for detecting tumor associated mutations in HBOC and is more sensitive than targeted panel sequencing. We are currently expanding our cohort to an additional 20 matched tumor pairs, including patients with pre-diagnosis plasma timepoints.

Citation Format: Derek Wong, Adriana Aguilar-Mahecha, Josiane Lafleur, Clarissa Chan, Kirsten Farncombe, Maia Norman, Leslie Oldfield, Prabhjit Basra, Stephanie Pederson, Johanna Wellum, Stephenie Prokopec, Mark Basik, Raymond H. Kim, Trevor Pugh. Cell-free whole genome sequencing for the detection of cancer in patients with germline BRCA1/2 mutations [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 538.

Surgical Management and Contralateral Breast Cancer Risk in Women with History of Radiation Therapy for Hodgkin Lymphoma: Results from a Population-Based Cohort

BACKGROUND

Women with history of chest irradiation for Hodgkin lymphoma are at increased risk of developing bilateral breast cancer, although contralateral breast cancer risk estimates in this population remain undefined.

METHODS

We queried the SEER database for women treated with radiation therapy for Hodgkin lymphoma prior to age 30 years and were diagnosed with a subsequent breast cancer between 1990-2016. Trends in surgical management and the 5- and 10-year cumulative incidence of contralateral breast cancer were evaluated.

RESULTS

The cohort included 295 women with a median age of 22 years (range 8-30 years) at Hodgkin lymphoma diagnosis, and 42 years (range 22-65 years) at breast cancer diagnosis. Overall, 263 (89.2%) presented with unilateral breast cancer, while 32 (10.8%) presented with synchronous bilateral breast cancer. Breast-conserving surgery was performed in 17.3% of patients, while mastectomy was performed in 82.7%. In 263 patients presenting with unilateral breast cancer, 50 (19.0%) underwent breast-conserving surgery and 213 (81.0%) underwent mastectomy. Subgroup analysis of mastectomy patients demonstrated a 40.5% bilateral mastectomy rate. The 5-year incidence of contralateral breast cancer in women who underwent unilateral surgery was 9.4% [95% confidence interval (CI), 5.6-15.4%], increasing to 20.2% (95% CI, 13.7-29.2%) at 10-year and 29.9% (95% CI, 20.8-41.9%) at 15-year follow-up.

CONCLUSIONS

Women with a history of prior chest radiation for Hodgkin lymphoma with a diagnosis of breast cancer have a 10-year contralateral breast cancer risk of 20%. These findings support consideration of contralateral prophylactic mastectomy during surgical decision-making for management of this high-risk patient population.

A novel immune cell signature predicts pathological complete response to neoadjuvant chemotherapy in triple negative breast cancer patients in the Q-CROC3 trial

e12614

Background: Tumor infiltrating lymphocytes (TILs) have been associated with good prognosis and response to neoadjuvant chemotherapy. Several reports have shown that the heterogeneity of tumor infiltrating immune cells affects the response to chemotherapy, with for example low levels of FOXP3 expressing T cells associated with good prognosis and pathological complete response (pCR) to chemotherapy. Methods: We examined different immune cell markers on 52 pre-chemotherapy biopsy specimens obtained from triple negative breast cancer patients undergoing neo-adjuvant chemotherapy from the Q-CROC-03 trial. Slides were stained for CD8, CD3,PD-1, PDL-1, FOXP-3 and Granzyme B using multi-colour immunohistochemistry and automated cell counting of stroma and epithelial counts was conducted using the Vectra/inForm image analysis platform. We had total of 39 variables for analysis and we performed Penalized logistic regression for variable selection. Results: Nine variables were found statistically significant to predict response to chemotherapy, PD1+ stroma counts being the one with the highest probability of association with response. A tree algorithm was then used on all 9 variables to identify the best variable and threshold combination to identify patients who respond to chemotherapy. We separated our cohort in test (25% of samples n = 13) and training (75% of samples n = 39) sets for this analysis. Restricting the tree depth to 2 variables for clinical interpretability identified the combination of average counts of stromal PD1+ and average density of stromal FOXP3+ as predictors of chemo response (accuracy 0.82). Both stromal average PD1+ counts and average stromal FOXP3+ density positively correlated with the levels of TILS. Conclusions: Combining FOXP3 and PD1 protein expression in the stroma of pre-treatment biopsies of triple negative breast cancers receiving neoadjuvant chemotherapy is highly predictive of pCR.

Incidence of Occult Breast Cancer in Carriers of BRCA1/2 or Other High-Penetrance Pathogenic Variants Undergoing Prophylactic Mastectomy: When is Sentinel Lymph Node Biopsy Indicated?

BACKGROUND

This study sought to determine the likelihood of occult malignancy during risk-reducing mastectomy in high-penetrance pathogenic variant carriers to help refine axillary staging recommendations.

METHODS

The authors performed a retrospective cohort study analyzing all female carriers of pathogenic variants in BRCA1/2, PALB2 or other genes who underwent prophylactic surgery at their institution between 2006 and 2021. Occult breast cancer was defined as the unanticipated presence of in situ or invasive malignancy on pathologic evaluation of prophylactic mastectomy specimens.

RESULTS

Of 523 women, 243 carriers met the inclusion criteria for the study including 124 BRCA1 (51.0%), 108 BRCA2 (44.4%), and 11 PALB2, TP53, CDH1, or PTEN (4.6%) carriers. The median age was 44 years (interquartile range, 37-52 years). Overall, 128 women (52.7%) underwent bilateral prophylactic mastectomies, and 115 (47.3%) underwent contralateral prophylactic mastectomy. In the 371 mastectomies performed, 16 (4.3%) occult malignancies were diagnosed. Most of the occult malignancies were ductal carcinoma in situ (13 mastectomies, 3.5%), whereas 3 mastectomies (0.8%) contained invasive breast cancer. If Breast Imaging Reporting and Data System (BIRADS) 1-2 or BIRADS 3 findings were reported on preoperative magnetic resonance imaging (MRI), the rate of occult malignancy decreased to 3.0 and 2.8%, respectively, per mastectomy. The patient-level factors associated with a likelihood of occult breast cancer greater than 10% included a history of prior breast cancer, age exceeding 60 years, and BIRADS 4 findings on preoperative imaging.

CONCLUSIONS

Occult invasive malignancy was detected in less than 1% of the risk-reducing mastectomies performed for women with BRCA1/2 or PALB2 pathogenic variants. Sentinel lymph node biopsy can be safely avoided when BIRADS 1-3 findings are reported on preoperative MRI.

Early Local Therapy for the Primary Site in De Novo Stage IV Breast Cancer: Results of a Randomized Clinical Trial (EA2108)

PURPOSE

Distant metastases are present in 6% or more of patients with newly diagnosed breast cancer. In this context, locoregional therapy for the intact primary tumor has been hypothesized to improve overall survival (OS), but clinical trials have reported conflicting results.

METHODS

Women presenting with metastatic breast cancer and an intact primary tumor received systemic therapy for 4-8 months; if no disease progression occurred, they were randomly assigned to locoregional therapy for the primary site (surgery and radiotherapy per standards for nonmetastatic disease) or continuing sysmetic therapy. The primary end point was OS; locoregional control and quality of life were secondary end points. The trial design provided 85% power to detect a 19.3% absolute difference in the 3-year OS rate in randomly assigned patients. The stratified log-rank test and Cox proportional hazards model were used to compare OS between arms. Cumulative incidence of locoregional progression was compared using Gray's test. Quality-of-life assessment used standard instruments.

RESULTS

Of 390 participants enrolled, 256 were randomly assigned: 131 to continued systemic therapy and 125 to early locoregional therapy. The 3-year OS was 67.9% without and 68.4% with early locoregional therapy (hazard ratio = 1.11; 90% CI, 0.82 to 1.52; P = .57). The median OS was 53.1 months (95% CI, 47.9 to not estimable) in the systemic therapy arm and 54.9 months (95% CI, 46.7 to not estimable) in the locoregional therapy arm. Locoregional progression was less frequent in those randomly assigned to locoregional therapy (3-year rate: 16.3% v 39.8%; P < .001). Quality-of-life measures were largely similar between arms.

CONCLUSION

Early locoregional therapy for the primary site did not improve survival in patients presenting with metastatic breast cancer. Although it was associated with improved locoregional control, this had no overall impact on quality of life.

Abstract PD7-07: Surgical management and contralateral breast cancer risk in women with a history of radiation therapy for Hodgkin lymphoma: Results from a population-based cohort

Background: Women with a history of chest radiation for Hodgkin lymphoma are at an increased risk of developing breast cancer. Although mastectomy has historically been recommended for surgical treatment of breast cancers in women with prior radiation exposure, surgical management trends and contralateral breast cancer risk in this population remain undefined. Methods: We performed a population-based retrospective study using the Surveillance, Epidemiology, and End Results (SEER) database from 1990-2016. Our cohort included women who received radiation for Hodgkin lymphoma prior to 30 years old and were diagnosed with a subsequent breast cancer. We evaluated trends in local therapy including rates of breast conserving surgery (BCS) and mastectomy. In those undergoing unilateral surgery, the Kaplan-Meier method was used to estimate the 5- and 10-year cumulative incidence of contralateral breast cancer. Results: Our final cohort included 295 women with a median age of 22 years (range, 8-30 years) at Hodgkin lymphoma diagnosis, and 42 years (range, 22-65 years) at breast cancer diagnosis. Of these patients, 263 (89.2%) presented with unilateral breast cancer, while 32 (10.8%) presented with synchronous bilateral breast cancer. Overall, BCS was performed in 17.3% of patients and mastectomy was performed in 82.7%. In the 263 patients presenting with unilateral breast cancer, 50 (19.0%) underwent BCS and 213 (81.0%) underwent mastectomy. Subgroup analysis of mastectomy patients with surgical laterality information available demonstrated a 40.5% bilateral mastectomy rate. In the entire cohort, the 5-year incidence of contralateral breast cancer in women who underwent unilateral surgery was 9.4% (95% CI, 5.6-15.4), increasing to 20.2% (95% CI, 13.7-29.2) at 10-years of follow up. Hormone receptor status of the index breast cancer was not associated with significant differences in the incidence of contralateral breast cancer (p=0.13). Conclusions: Women with a history of prior chest radiation for Hodgkin Lymphoma with a diagnosis with breast cancer have a 10-year contralateral breast cancer risk of 20%. These findings support consideration of contralateral prophylactic mastectomy during surgical decision-making in this high-risk patient population.

Citation Format: Elisheva R Eisenberg, Anna Weiss, Ipshita Prakash, Sonia Skamene, Mark Basik, Jean Francois Boileau, Lissa Ajjamada, Michael Pollak, Stephanie M Wong. Surgical management and contralateral breast cancer risk in women with a history of radiation therapy for Hodgkin lymphoma: Results from a population-based cohort [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 PD7-07.

HSP90 inhibitors induce GPNMB cell-surface expression by modulating lysosomal positioning and sensitize breast cancer cells to glembatumumab vedotin

Transmembrane glycoprotein NMB (GPNMB) is a prognostic marker of poor outcome in patients with triple-negative breast cancer (TNBC). Glembatumumab Vedotin, an antibody drug conjugate targeting GPNMB, exhibits variable efficacy against GPNMB-positive metastatic TNBC as a single agent. We show that GPNMB levels increase in response to standard-of-care and experimental therapies for multiple breast cancer subtypes. While these therapeutic stressors induce GPNMB expression through differential engagement of the MiTF family of transcription factors, not all are capable of increasing GPNMB cell-surface localization required for Glembatumumab Vedotin inhibition. Using a FACS-based genetic screen, we discovered that suppression of heat shock protein 90 (HSP90) concomitantly increases GPNMB expression and cell-surface localization. Mechanistically, HSP90 inhibition resulted in lysosomal dispersion towards the cell periphery and fusion with the plasma membrane, which delivers GPNMB to the cell surface. Finally, treatment with HSP90 inhibitors sensitizes breast cancers to Glembatumumab Vedotin in vivo, suggesting that combination of HSP90 inhibitors and Glembatumumab Vedotin may be a viable treatment strategy for patients with metastatic TNBC.

OUP accepted manuscript

Background

We explored health professionals’ views on the utility of circulating tumor DNA (ctDNA) testing in hereditary cancer syndrome (HCS) management.

Materials and Methods

A qualitative interpretive description study was conducted, using semi-structured interviews with professionals across Canada. Thematic analysis employing constant comparison was used for analysis. 2 investigators coded each transcript. Differences were reconciled through discussion and the codebook was modified as new codes and themes emerged from the data.

Results

Thirty-five professionals participated and included genetic counselors (n = 12), geneticists (n = 9), oncologists (n = 4), family doctors (n = 3), lab directors and scientists (n = 3), a health-system decision maker, a surgeon, a pathologist, and a nurse. Professionals described ctDNA as “transformative” and a “game-changer”. However, they were divided on its use in HCS management, with some being optimistic (optimists) while others were hesitant (pessimists). Differences were driven by views on 3 factors: (1) clinical utility, (2) ctDNA’s role in cancer screening, and (3) ctDNA’s invasiveness. Optimists anticipated ctDNA testing would have clinical utility for HCS patients, its role would be akin to a diagnostic test and would be less invasive than standard screening (eg imaging). Pessimistic participants felt ctDNA testing would add limited utility; it would effectively be another screening test in the pathway, likely triggering additional investigations downstream, thereby increasing invasiveness.

Conclusions

Providers anticipated ctDNA testing will transform early cancer detection for HCS families. However, the contrasting positions on ctDNA’s role in the care pathway raise potential practice variations, highlighting a need to develop evidence to support clinical implementation and guidelines to standardize adoption.

Clinicopathologic features of breast cancers diagnosed in women treated with prior radiation therapy for Hodgkin lymphoma: Results from a population-based cohort

BACKGROUND

Childhood and young adult survivors of Hodgkin lymphoma (HL) are at elevated risk of developing breast cancer, yet little data exist on the tumor characteristics that develop in this high-risk patient population.

METHODS

The National Cancer Institute's Surveillance, Epidemiology, and End Results database was used to identify breast cancers diagnosed between 1990 and 2016 in women who had received prior radiation therapy for HL at age 30 years or younger. Clinicopathologic features of subsequent breast cancers (breast cancer after radiation therapy for HL [BC-HL]) were examined and compared with breast cancers diagnosed in women who had no prior malignancy (breast cancer with no prior malignancy [BC-NPM]).

RESULTS

In total, 321 breast cancers were identified in 257 women who had a history of radiation therapy for HL. The median age at HL diagnosis was 22 years (interquartile range, 18-26 years), and nearly all patients in the BC-HL group (97.9%) were diagnosed ≥8 years after radiation therapy. Overall, 56 patients in the BC-HL group (21.8%) developed bilateral breast cancer. Compared with women who had BC-NPM, those who had BC-HL were younger (43 vs 60 years; P < .001) and were less likely to present with ductal carcinoma in situ (8.4% vs 14.9%; P = .001). On multivariable analysis that included adjustment for age, invasive BC-HL was associated with smaller (≤2 cm) tumor size (odds ratio, 1.64; 95% CI, 1.25-2.15) and upper outer quadrant tumors (odds ratio, 1.37; 95% CI, 1.04-1.81) compared with BC-NPM. In a subset analysis of 102 women who had HER2/neu status available, the distribution of biologic subtype was not significantly different between BC-HL and BC-NPM (P = .16).

CONCLUSIONS

Breast cancers in women who previously received radiation therapy for HL are characterized by earlier onset disease, although most remain estrogen receptor-positive and have early stage disease at presentation.

LAY SUMMARY

Women who have had radiation therapy for Hodgkin lymphoma at a young age are at increased risk of developing early onset breast cancer; however, most of these breast cancers are sensitive to hormones (estrogen receptor-positive) and are diagnosed at early stages. Because these breast tumors are estrogen receptor-positive, medications that prevent breast cancer by blocking the effect of or lowering hormone levels (also termed endocrine prevention) may be useful in this group of high-risk women.

Healthcare policy by other means: Cancer clinical research as "oncopolicy"

Social studies of biomedicine often focus on how exogenous policies shape the medical domain. While policy agendas no doubt affect complex biomedical projects, in the present paper we analyze a different dynamic, namely how oncologists enact policy as part of several flagship precision oncology endeavors. Empirically, the article focuses on the U.S. TAPUR trial, the Dutch DRUP trial, and the Canadian CAPTUR trial, which have recently been joined by similar Scandinavian studies. Taken together, these trials represent innovative forms of clinical research that, beyond their varying experimental nature, have been designed to transform the evidential processes to provide access to biomarker-driven treatments. Along with gathering evidence on effectiveness of off-label targeted therapies, their explicit goals include the recentering of a major professional organization around research, and the reframing of healthcare as a learning system seamlessly connecting epistemic, organizational, and economic issues. Accordingly, we analyze the design and implementation of these trials as a form of (onco)policy by other means.

A multiplexed, automated immuno-matrix assisted laser desorption/ionization mass spectrometry assay for simultaneous and precise quantitation of PTEN and p110α in cell lines and tumor tissues

The PI3-kinase/AKT/mTOR pathway plays a central role in cancer signaling. While p110α is the catalytic α-subunit of PI3-kinase and a major drug target, PTEN is the main negative regulator of the PI3-kinase/AKT/mTOR pathway. PTEN is often down-regulated in cancer, and there are conflicting data on PTEN's role as breast cancer biomarker. PTEN and p110α protein expression in tumors is commonly analyzed by immunohistochemistry, which suffers from poor multiplexing capacity, poor standardization, and antibody crossreactivity, and which provides only semi-quantitative data. Here, we present an automated, and standardized immuno-matrix-assisted laser desorption/ionization mass spectrometry (iMALDI) assay that allows precise and multiplexed quantitation of PTEN and p110α concentrations, without the limitations of immunohistochemistry. Our iMALDI assay only requires a low-cost benchtop MALDI-TOF mass spectrometer, which simplifies clinical translation. We validated our assay's precision and accuracy, with simultaneous enrichment of both target proteins not significantly affecting the precision and accuracy of the quantitation when compared to the PTEN- and p110α-singleplex iMALDI assays (<15% difference). The multiplexed assay's linear range is from 0.6-20 fmol with accuracies of 90-112% for both target proteins, and the assay is free of matrix-related interferences. The inter-day reproducibility over 5-days was high, with an overall CV of 9%. PTEN and p110α protein concentrations can be quantified down to 1.4 fmol and 0.6 fmol per 10 μg of total tumor protein, respectively, in various tumor tissue samples, including fresh-frozen breast tumors and colorectal cancer liver metastases, and patient-derived xenograft (PDX) tumors.

Population-based analysis of non-operative management and treatment patterns in older women with estrogen receptor-positive breast cancer

PURPOSE

To examine the proportion of older women with ER + HER2- breast cancer receiving non-operative management versus surgery, and to evaluate the use of axillary staging and adjuvant radiation in this population.

METHODS

We queried the SEER database to identify all women aged 70 years or older with stage I-III ER + HER2- invasive breast cancer diagnosed between 2010 and 2016. We evaluated trends in non-operative management, breast surgery, axillary staging, and adjuvant radiation according to age at diagnosis.

RESULTS

We identified 57,351 older women with ER + HER2- disease. Overall, 3538 (6.2%) of the cohort underwent non-operative management, 38,452 (67.0%) underwent breast-conserving surgery (BCS), and 15,361 (26.8%) underwent mastectomy. The proportion of patients undergoing non-operative management increased from 2.8% among 70-74-year-old women to 30.1% in those ≥ 90 years old (p < 0.001). In 53,813 women who underwent surgery, 36,850 (68.5%) underwent sentinel lymph node biopsy, while 10,861 (20.2%) underwent axillary lymph node dissection. Subgroup analysis of 29,032 older women undergoing BCS for stage I ER + HER2- breast cancer revealed a 14.2% rate of omission of axillary staging, increasing from 5.3% in those 70-74 years to 67.6% in those ≥ 90 years old (p < 0.001). Receipt of adjuvant radiation occurred in 63.3% of older women following BCS and 18% post-mastectomy, with similar trends towards omission in older age groups.

CONCLUSION

Primary breast surgery remains the dominant management strategy for the majority of older women with ER + HER2- breast cancer. Omission of axillary staging and adjuvant radiation are used in a minority of eligible women undergoing breast conservation for early-stage disease.

Precise Quantitation of PTEN by Immuno-MRM: A Tool To Resolve the Breast Cancer Biomarker Controversy

The tumor suppressor PTEN is the main negative regulator of PI3K/AKT/mTOR signaling and is commonly found downregulated in breast cancer (BC). Conflicting data from conventional immunoassays such as immunohistochemistry (IHC) has sparked controversy about PTEN's role as a prognostic and predictive biomarker in BC, which can be largely attributed to the lack of specificity, sensitivity, and interlaboratory standardization. Here, we present a fully standardized, highly sensitive, robust microflow immuno-MRM (iMRM) assay that enables precise quantitation of PTEN concentrations in cells and fresh frozen (FF) and formalin-fixed paraffin-embedded (FFPE) tissues, down to 0.1 fmol/10 μg of extracted protein, with high interday and intraday precision (CV 6.3%). PTEN protein levels in BC PDX samples that were determined by iMRM correlate well with semiquantitative IHC and WB data. iMRM, however, allowed the precise quantitation of PTEN-even in samples that were deemed to be PTEN negative by IHC or western blot (WB)-while requiring substantially less tumor tissue than WB. This is particularly relevant because the extent of PTEN downregulation in tumors has been shown to correlate with severity. Our standardized and robust workflow includes an 11 min microflow LC-MRM analysis on a triple-quadrupole MS and thus provides a much needed tool for the study of PTEN as a potential biomarker for BC.

Clinicopathologic features of breast cancers diagnosed in females treated with prior radiation therapy for Hodgkin lymphoma: Results from a population-based cohort

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Background: Childhood and young adult survivors of Hodgkin Lymphoma are at an increased risk of developing breast cancer, although little data exist on the characteristics and biologic subtype of breast cancers that develop in this high-risk population. Methods: The Surveillance, Epidemiology, and End Results (SEER) database was used to identify all histologically confirmed breast cancers diagnosed between 1990-2016 in women treated with prior radiation therapy for Hodgkin Lymphoma ≤ 30 years of age. Clinicopathologic features of subsequent breast cancers (BC-HL) were examined and compared to breast cancers diagnosed in women with no prior malignancy (BC-NPM). The association between prior chemotherapy use and biologic subtype of BC-HL was evaluated. Results: We identified 321 breast cancers diagnosed in 257 women with a history of radiation therapy for Hodgkin Lymphoma. The median age at Hodgkin Lymphoma diagnosis was 22 years (range, 12-30 years), and nearly all BC-HL (97.9%) were diagnosed 8 or more years after radiation therapy. Overall, 56 (21.8%) BC-HL patients developed bilateral breast cancer, of which 28 (50%) were synchronous. When compared to women with BC-NPM, women with BC-HL were significantly younger at time of diagnosis (median age, 43 years vs. 60 years, p<0.001) and less likely to present with ductal carcinoma in situ (8.4% vs. 14.9%, p=0.001). Patients with invasive BC-HL were more likely to have high grade (43.8% vs. 32.9%, p<0.001), estrogen receptor (ER) negative breast cancer (27.7% vs. 18.2%, p<0.001), although pathologic tumor size, nodal status, and stage were not significantly different from those with BC-NPM. Compared to women with BC-NPM, the majority of operable BC-HL patients underwent surgical management with mastectomy (86.5% vs. 42.5%, p<0.001). In subset analysis of 102 women for which HER2 status was available, BC-HL were HER2+ in 18.7% of patients. Distribution of biologic subtype between BC-HL and BC-NPM are shown in the table below. In BC-HL patients, prior chemotherapy exposure was not associated with substantial differences in the proportion of ER+HER2- breast cancers (65.8% vs. 63.5%, p=0.82). Conclusions: Breast cancers in women treated with radiation therapy for Hodgkin Lymphoma are characterized by earlier onset and more aggressive biologic features, although the majority remain estrogen sensitive and early stage at presentation. Further studies are warranted to evaluate the use of preventive strategies in this high-risk patient population.[Table: see text]

The MNK1/2-eIF4E Axis Supports Immune Suppression and Metastasis in Postpartum Breast Cancer

Breast cancer diagnosed within 10 years following childbirth is defined as postpartum breast cancer (PPBC) and is highly metastatic. Interactions between immune cells and other stromal cells within the involuting mammary gland are fundamental in facilitating an aggressive tumor phenotype. The MNK1/2-eIF4E axis promotes translation of prometastatic mRNAs in tumor cells, but its role in modulating the function of nontumor cells in the PPBC microenvironment has not been explored. Here, we used a combination of in vivo PPBC models and in vitro assays to study the effects of inactivation of the MNK1/2-eIF4E axis on the protumor function of select cells of the tumor microenvironment. PPBC mice deficient for phospho-eIF4E (eIF4E^S209A) were protected against lung metastasis and exhibited differences in the tumor and lung immune microenvironment compared with wild-type mice. Moreover, the expression of fibroblast-derived IL33, an alarmin known to induce invasion, was repressed upon MNK1/2-eIF4E axis inhibition. Imaging mass cytometry on PPBC and non-PPBC patient samples indicated that human PPBC contains phospho-eIF4E high-expressing tumor cells and CD8⁺ T cells displaying markers of an activated dysfunctional phenotype. Finally, inhibition of MNK1/2 combined with anti-PD-1 therapy blocked lung metastasis of PPBC. These findings implicate the involvement of the MNK1/2-eIF4E axis during PPBC metastasis and suggest a promising immunomodulatory route to enhance the efficacy of immunotherapy by blocking phospho-eIF4E. SIGNIFICANCE: This study investigates the MNK1/2-eIF4E signaling axis in tumor and stromal cells in metastatic breast cancer and reveals that MNK1/2 inhibition suppresses metastasis and sensitizes tumors to anti-PD-1 immunotherapy.

Abstract PS4-48: Development of a multiplexed protein panel using a targeted proteomics approach for the study of CDK4/6 inhibitors resistance in hormone receptor positive breast cancer

Background Breast cancer is the most common malignancy in woman and hormone receptor positive breast cancer represents approximately 70% of all cases. These patients are treated with endocrine therapies aimed at disrupting hormone receptor signaling and estrogen production which improves survival and allows a cure in early stages. However, recurrent disease, metastatic dissemination and drug resistance limit the survival of patients. The limitations regarding endocrine therapy have prompted the search for new therapeutic targets, such as CDK4/6 Inhibitors. Despite the improved disease control that CDK4/6 Inhibitors offer to patients, not all patients respond to these drugs and some patients whose tumors respond to CDK4/6 Inhibitors eventually develop acquired resistance. No proven biomarkers of CDK4/6 Inhibitors efficacy exist to date, and there is a need for diagnostic tools that could stratify patients to save costs and the burden of unnecessary therapy. Our aim is to perform a quantitative evaluation of marker proteins with a developed multiplexed panel using targeted mass spectrometry (MS)-based proteomics for 25 proteins from the CDK/RB/E2F-pathway which have been shown in the literature to be central to CDK4/6I resistance. Material and Methods We developed Multiple Reaction Monitoring (MRM) MS methods for the 25 target proteins from the CDK/RB/E2F-pathway using synthetic heavy-isotope-labeled standards with the aim of creating MRM assays to enable specific, sensitive and precise quantitation of these proteins in small amounts of cell line and tissue samples. Moreover, we developed a high resolution peptide fractionation system using high-pH micro-flow liquid chromatography (LC) which is required to overcome the problem of small samples amounts while improving analytical assay sensitivity in the analysis of complex biological matrices such as breast cancer biopsies. The MCF-7 human breast cancer cell line was used as model during method development. Proteins from cell lysates were isolated, reduced, alkylated and digested with trypsin. The resulting tryptic peptides were micro-flow fractionated into 70 fractions and the developed nano-LC-MS MRM assays were used for peptide detection and quantification. Data were analyzed using Skyline. Results Our developed micro-flow fractionation method allowed us to work on limited amounts of samples (60ug), and increased the possibility to detecting low abundance proteins such as cell cycle components. Using the MCF-7 cell model, we are able to identify and quantify 17 proteins out of the 25 from our panel: CDK1, CDK2, CDK4, Cyclin B1, Cyclin D1, Cyclin D3, Cyclin E1, RB1, E2F-3, E2F-4, E2F-5, ESR1, TOP2A, TYMS, EZH2, MKI67, BIRC5. Conclusion We have developed a highly specific MS-based multiplexed assay with peptide standards targeting 25 proteins relevant to CDK4/6 Inhibitors breast cancer treatment. Our micro-flow fractionation method increased assay sensitivity and allows for the analysis of small sample amounts. In the future we will apply this workflow to samples such as Patient Derived Xenografts models, breast cancer tissues and FFPE samples in order to identify the predictive value of these potential biomarkers for responsiveness to CDK4/6 Inhibitors.

Citation Format: Marta Zurawska, Adriana Aguilar-Mahecha, Mark Basik, Michal Dadlez, Dominik Domanski. Development of a multiplexed protein panel using a targeted proteomics approach for the study of CDK4/6 inhibitors resistance in hormone receptor positive breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-48.

Sequential use of Antibiotics and Adjuvant Chemotherapy Leading to a Fatal Pseudomembranous Colitis

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Oncologic Safety of Sentinel Lymph Node Biopsy Alone After Neoadjuvant Chemotherapy for Breast Cancer

BACKGROUND

The oncologic safety of sentinel lymph node biopsy (SLNB) alone for clinically node-positive (cN1-2) patients who convert to pathologic node-negativity (ypN0) after neoadjuvant chemotherapy (NAC) is not well established.

METHODS

This study retrospectively identified 244 consecutive patients with a diagnosis of cT1-3cN0-2 breast cancer who underwent NAC followed by SLNB at the authors' institution between 2013 and 2018. The patients were categorized as clinically node-negative (cN0) or cN1-2 before the onset of NAC, and the Kaplan-Meier method was used to compare locoregional and distant recurrence rates after SLNB alone for ypN0 patients.

RESULTS

Among 244 patients who underwent NAC followed by surgery with SLNB for axillary staging, 112 (45.9%) were cN0 at presentation, whereas 132 (54.5%) had biopsy-proven cN1-2 disease and converted to cN0 after treatment. Of the patients presenting with cN0 disease, 102 (91.1%) were ypN0 on SLNB pathology compared with 60 cN1/2 patients (45.5%; p < 0.001). Regional nodal irradiation was administered to 5% of the cN0/ypN0 patients compared with 70.7% of the cN1-2/ypN0 patients (p < 0.001). Overall, 211 patients were treated with SLNB alone and had a median follow-up period of 36 months (interquartile range [IQR], 24-53 months). For 101 cN0/ypN0 patients who underwent SLNB alone, the 5-year local and regional recurrence rates were respectively 5.7% (95% confidence interval [CI], 2.4-13.8) and 1% (95% CI 0.1-7.0). For 58 cN1-2/ypN0 patients who underwent SLNB alone, the 5-year local and regional recurrence rates were respectively 4.1% (95% CI 1.0-15.5) and 0%, with no axillary recurrences noted.

CONCLUSION

For ypN0 patients, SLNB alone after NAC is associated with low and acceptable short-term axillary recurrence rates. Additional follow-up data from prospective clinical trials are needed to confirm long-term oncologic safety and define optimal local therapy recommendations.

Abstract B21: Protein quantitation assays for Akt, PI3K p110α, and PTEN to assess PI3K pathway activity in tumor tissue

Introduction: Many clinical trials for inhibitors targeting the PI3K pathway now include genetic screening of tumors to try to select probable treatment responders. Genetic testing identifies some relevant mutations, but this approach does not address many mechanisms of PI3K pathway regulation. Epigenetic changes and post-translational modifications may increase pathway activity without any detectable DNA mutation. Where mutations are detected, mutated proteins may not be expressed or may be quickly degraded. Direct measurement of oncogenic proteins may therefore offer more useful molecular profiles for characterizing cancer-driving alterations and matching patients with appropriate treatments.

Purpose: The purpose of this study was to develop and implement protein quantitation assays to accurately assess PI3K pathway activity in tumors, as a means of matching patients with targeted cancer treatments.

Methods: Protein extracted from tumor tissue lysate is subjected to proteolytic digestion to generate proteotypic peptides used for protein quantitation. Synthetic stable isotope-labeled peptides are added to the digest as an internal standard, after which the target peptides are immuno-enriched with antibodies coupled to magnetic beads. MS analysis is then performed by either eluting peptides for measurement with liquid chromatography multiple reaction monitoring tandem MS (LC-MRM-MS/MS) or by spotting beads onto a plate for matrix-assisted laser desorption MS (MALDI-MS). External calibration curves are used for accurate quantitation.

Results: We developed and implemented MS-based methods to determine the concentration of PI3K pathway proteins in tumor samples. The developed methods enable precise and reproducible quantitation of Akt1, Akt2, PI3K P110α, and PTEN. We were able to distinguish and quantify specific isoforms, including phospho-Akt1 (Ser473), phospho-Akt2 (Ser474), and mutant-Akt (E17K). Endogenous protein levels were quantified in cell lines, fresh-frozen tumor samples, and formalin-fixed, paraffin embedded tumor tissue. 10 μg of protein extract per analyte was sufficient for quantitation. Subsets of assays could be multiplexed through simultaneous or sequential enrichment without compromising assay performance.

Novel Aspect: The multiplexing of immuno-MALDI assays through sequential enrichment and the immuno-MRM-MS assays for PTEN and mutant Akt represent new developments. Recent adoption of monoclonal antibodies for Akt1 will facilitate this assay's translation to a clinical setting.

Conclusions: This panel of quantitative proteomics assays enables comprehensive PI3K pathway assessment in tumor tissues. Previously collected genetically screened tumor samples were obtained with patient consent (as approved by the Jewish General Hospital Research Ethics Committee). Samples will be analyzed to assess PI3K pathway activity and determine its correlation to clinical features and response to PI3K-targeted treatments.

Note: This abstract was not presented at the conference.

Citation Format: Constance A. Sobsey, Robert Popp, Sahar Ibrahim, Bjoern C Froehlich, Adriana Aguilar-Mahecha, Mark Basik, Gerald Batist, Christoph Borchers. Protein quantitation assays for Akt, PI3K p110α, and PTEN to assess PI3K pathway activity in tumor tissue [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr B21.

Prognostic and predictive value of circulating tumor DNA during neoadjuvant chemotherapy for triple negative breast cancer

Response to neoadjuvant chemotherapy (NAC) in triple negative breast cancer (TNBC) is highly prognostic and determines whether adjuvant chemotherapy is needed if residual tumor is found at surgery. To evaluate the predictive and prognostic values of circulating tumor DNA (ctDNA) in this setting, we analyzed tumor and serial bloods from 26 TNBC patients collected prior, during, and after NAC. Individual digital droplet PCR assays were developed for 121 variants (average 5/patient) identified from tumor sequencing, enabling ctDNA detection in 96% of patients at baseline. Mutant allele frequency at baseline was associated with clinical characteristics. Levels drastically fell after one cycle of NAC, especially in patients whose tumors would go on to have a pathological complete response (pCR), but then rose significantly before surgery in patients with significant residual tumor at surgery (p = 0.0001). The detection of ctDNA early during treatment and also late at the end of NAC before surgery was strongly predictive of residual tumor at surgery, but its absence was less predictive of pCR, especially when only TP53 variants are considered. ctDNA detection at the end of neoadjuvant chemotherapy indicated significantly worse relapse-free survival (HR = 0.29 (95% CI 0.08–0.98), p = 0.046), and overall survival (HR = 0.27 95% CI 0.075–0.96), p = 0.043). Hence, individualized multi-variant ctDNA testing during and after NAC prior to surgery has prognostic and predictive value in early TNBC patients.

Systematic Optimization of the iMALDI Workflow for the Robust and Straightforward Quantification of Signaling Proteins in Cancer Cells

PURPOSE

Immuno-MALDI (iMALDI) combines immuno-enrichment of biomarkers with MALDI-MS for fast, precise, and specific quantitation, making it a valuable tool for developing clinical assays. iMALDI assays are optimized for the PI3-kinase signaling pathway members phosphatase and tensin homolog (PTEN) and PI3-kinase catalytic subunit alpha (p110α), with regard to sensitivity, robustness, and throughput. A standardized template for developing future iMALDI assays, including automation protocols to streamline assay development and translation, is provided.

EXPERIMENTAL DESIGN

Conditions for tryptic digestion and immuno-enrichment (beads, bead:antibody ratios, incubation times, direct vs. indirect immuno-enrichment) are rigorously tested. Different strategies for calibration and data readout are compared.

RESULTS

Digestion using 1:2 protein:trypsin (wt:wt) for 1 h yielded high and consistent peptide recoveries. Direct immuno-enrichment (antibody-bead coupling prior to antigen-enrichment) yielded 30% higher peptide recovery with a 1 h shorter incubation time than indirect enrichment. Immuno-enrichment incubation overnight yielded 1.5-fold higher sensitivities than 1 h incubation. Quantitation of the endogenous target proteins is not affected by the complexity of the calibration matrix, further simplifying the workflow.

CONCLUSIONS AND CLINICAL RELEVANCE

This optimized and automated workflow will facilitate the clinical translation of high-throughput sensitive iMALDI assays for quantifying cell-signaling proteins in individual tumor samples, thereby improving patient stratification for targeted treatment.

Breast cancer mammospheres secrete Adrenomedullin to induce lipolysis and browning of adjacent adipocytes

Background

Cancer cells cooperate with cells that compose their environment to promote tumor growth and invasion. Among them, adipocytes provide lipids used as a source of energy by cancer cells and adipokines that contribute to tumor expansion. Mechanisms supporting the dynamic interactions between cancer cells and stromal adipocytes, however, remain unclear.

Methods

We set-up a co-culture model with breast cancer cells grown in 3D as mammospheres and human adipocytes to accurately recapitulate intrinsic features of tumors, such as hypoxia and cancer cell–adipocytes interactions.

Results

Herein, we observed that the lipid droplets’ size was reduced in adipocytes adjacent to the mammospheres, mimicking adipocyte morphology on histological sections. We showed that the uncoupling protein UCP1 was expressed in adipocytes close to tumor cells on breast cancer histological sections as well as in adipocytes in contact with the mammospheres.

Mammospheres produced adrenomedullin (ADM), a multifactorial hypoxia-inducible peptide while ADM receptors were detected in adipocytes. Stimulation of adipocytes with ADM promoted UCP1 expression and increased HSL phosphorylation, which activated lipolysis. Invalidation of ADM in breast cancer cells dramatically reduced UCP1 expression in adipocytes.

Conclusions

Breast tumor cells secreted ADM that modified cancer–associated adipocytes through paracrine signaling, leading to metabolic changes and delipidation. Hence, ADM appears to be crucial in controlling the interactions between cancer cells and adipocytes and represents an excellent target to hinder them.