LobSig is a multigene predictor of outcome in invasive lobular carcinoma

Co-regulator activity of Mediator of DNA Damage Checkpoint 1 (MDC1) is associated with DNA repair dysfunction and PARP inhibitor sensitivity in lobular carcinoma of the breast

Invasive lobular carcinoma of the breast (ILC) is typically estrogen receptor α (ER)-positive and presents with biomarkers of anti-estrogen sensitive disease, yet patients with ILC face particularly poor long-term outcomes with increased recurrence risk, suggesting endocrine response and ER function are unique in ILC. ER is co-regulated by the DNA repair protein Mediator of DNA Damage Checkpoint 1 (MDC1) specifically in ILC cells, driving distinct ER activity. However, this novel MDC1 activity is associated with dysfunctional canonical DNA repair activity by MDC1, but without typical features of DNA repair deficiency. To understand reciprocal activities of MDC1, we profiled the MDC1 interactome and found MDC1-associated proteins in ILC cells mirror a "BRCA-like" state lacking key homologous recombination (HR) proteins, consistent with HR dysfunction but distinct from classic "BRCAness". HR dysfunction in ILC cells is supported by single-cell transcriptome and DNA repair activity analyses, with DNA repair signaling and functional data, showing dysfunctional induction and resolution of HR. In parallel, ILC tumor data are consistent with a distinct form of HR dysfunction via impaired HR resolution, lacking BRCA-like genomic scarring but showing elevated signatures of PARP inhibitor sensitivity. We demonstrate this HR dysfunction can be exploited using PARP inhibition, and found that talazoparib treatment produced a durable growth suppression both in vitro and in multiple ILC xenografts in vivo. ILC-specific ER:MDC1 activity creates a new context for ER and MDC1 function in ILC, at the cost of a DNA repair dysfunction, which may be therapeutically targetable.

Survival outcomes for patients with invasive lobular cancer by MammaPrint: Results from the MINDACT phase III trial

BACKGROUND

Evaluation of the prognostic performance and clinical utility of the MammaPrint 70-gene signature in early-stage invasive lobular carcinoma (ILC) for whom such analyses in a randomized trial is awaited.

PATIENTS AND METHODS

Exploratory subgroup analysis of MINDACT trial patients with centrally assessed histology (n = 5929) with invasive breast cancer of no-special-type (NST), or pure ILC. In the trial patients were categorized based on the 70-gene signature for genomic risk and modified Adjuvant!Online for clinical risk. Survival outcomes at 8.7 years median follow-up by 70-gene signature were compared between NST and ILC for Distant Metastasis-Free Survival (DMFS), Disease-Free Survival (DFS) and Overall Survival (OS).

RESULTS

5313 patients were ILC (n = 487) or NST (n = 4826). ILC was further classified into classic ILC (n = 255) or ILC variants (n = 232). The 70-gene signature classified 16.2 % of ILC and 39.1 % of NST as genomic high-risk (gH). Survival outcomes for ILC vs. NST revealed similar estimates according to genomic risk overall and across subsets. The 70-gene signature classified 10.2 % of classic ILC and 22.8 % of ILC variants as gH. 5-yr DFS estimates for ILC variants 88.4 % (95 %CI: 83.1-92.1) was inferior to classic ILC 93.0 % (95 %CI: 88.7-95.7).

CONCLUSIONS

Sixteen percent of ILC were classified high genomic risk by the 70-gene signature, with unfavorable survival outcomes. Survival estimates were similar for patients with ILC and NST classified as either low- or high-genomic risk, suggesting that the 70-gene signature also has prognostic value in ILC and may be a clinically useful tool for adjuvant treatment decision-making in ILC.

A pooled analysis evaluating prognostic significance of Residual Cancer Burden in invasive lobular breast cancer

Residual Cancer Burden (RCB) after neoadjuvant chemotherapy (NAC) is validated to predict event-free survival (EFS) in breast cancer but has not been studied for invasive lobular carcinoma (ILC). We studied patient-level data from a pooled cohort across 12 institutions. Associations between RCB index, class, and EFS were assessed in ILC and non-ILC with mixed effect Cox models and multivariable analyses. Recursive partitioning was used in an exploratory model to stratify prognosis by RCB components. Of 5106 patients, the diagnosis was ILC in 216 and non-ILC in 4890. Increased RCB index was associated with worse EFS in both ILC and non-ILC (p = 0.002 and p < 0.001, respectively) and remained prognostic when stratified by receptor subtype and adjusted for age, grade, T category, and nodal status. Recursive partitioning demonstrated residual invasive cancer cellularity as most prognostic in ILC. These results underscore the utility of RCB for evaluating NAC response in those with ILC.

The Challenges of Lobular Carcinomas from a Surgeon's Point of View

Invasive lobular breast cancer (ILC) presents unique challenges and considerations in the realm of surgical management. Characterized by its distinct histological features, including the loss of E-cadherin expression and dys-cohesive growth pattern, ILC often poses diagnostic and therapeutic dilemmas for clinicians. This abstract explores the surgical landscape of ILC, focusing on its epidemiology, clinical presentation, diagnostic modalities, and surgical interventions. Emphasizing the importance of individualized treatment strategies, this narrative delves into the nuances of surgical decision-making, including the role of breast-conserving surgery versus mastectomy, axillary staging, and the significance of margin status. Additionally, advancements in surgical techniques, such as oncoplastic approaches and sentinel lymph node biopsy, are examined in the context of optimizing oncologic outcomes and preserving cosmesis. Through a comprehensive review of current literature and clinical guidelines, this overview aims to provide a nuanced understanding of the surgical considerations inherent to the management of invasive lobular breast cancer.

Nomograms to predict the long-term prognosis for non-metastatic invasive lobular breast carcinoma: a population-based study

Invasive lobular breast carcinoma (ILC) is one potential subset that "clinicopathologic features" can conflict with "long-term outcome" and the optimal management strategy is unknown in such discordant situations. The present study aims to predict the long-term, overall survival (OS) and cancer-specific survival (CSS) of ILC. The clinical information of patients with non-metastatic ILC was retrieved from the Surveillance, Epidemiology, and End Results (SEER) database between 2004 and 2020. A total of 31451 patients were enrolled and divided into the training cohort (n=22,017) and validation cohort (n=9434). The last follow-up was December, 31, 2020 and the median follow-up period was 99 months (1-203). Age, marriage, estrogen (ER) status, progesterone (PR) status, grade, tumor size, lymph node ratio (LNR) and combined summary (CS) stage were prognostic factors for both OS and CSS of ILC, whereas chemotherapy and radiation were independent protect factors for OS. The nomograms exhibited satisfactory discriminative ability. For the training and validation cohorts, the C-index of the OS nomogram was 0.765 (95% CI 0.762-0.768) and 0.757 (95% CI 0.747-0.767), and the C-index of the CSS nomogram were 0.812 (95% CI 0.804-0.820) and 0.813 (95% CI 0.799-0.827), respectively. Additionally, decision curve analysis (DCA) demonstrated that the nomograms had superior predictive performance than traditional American Joint Committee on Cancer (AJCC) TNM stage. The novel nomograms to predict long-term prognosis based on LNR are reliable tools to predict survival, which may assist clinicians in identifying high-risk patients and devising individual treatments for patients with ILC. Our findings should aid public health prevention strategies to reduce cancer burden. We provide two R/Shiny apps ( https://ilc-survival2024.shinyapps.io/osnomogram/ ; https://ilc-survival2024.shinyapps.io/cssnomogram/ ) to visualize findings.

Pathway-based signatures predict patient outcome, chemotherapy benefit and synthetic lethal dependencies in invasive lobular breast cancer

BACKGROUND

Invasive Lobular Carcinoma (ILC) is a morphologically distinct breast cancer subtype that represents up to 15% of all breast cancers. Compared to Invasive Breast Carcinoma of No Special Type (IBC-NST), ILCs exhibit poorer long-term outcome and a unique pattern of metastasis. Despite these differences, the systematic discovery of robust prognostic biomarkers and therapeutically actionable molecular pathways in ILC remains limited.

METHODS

Pathway-centric multivariable models using statistical machine learning were developed and tested in seven retrospective clinico-genomic cohorts (n = 996). Further external validation was performed using a new RNA-Seq clinical cohort of aggressive ILCs (n = 48).

RESULTS AND CONCLUSIONS

mRNA dysregulation scores of 25 pathways were strongly prognostic in ILC (FDR-adjusted P < 0.05). Of these, three pathways including Cell-cell communication, Innate immune system and Smooth muscle contraction were also independent predictors of chemotherapy response. To aggregate these findings, a multivariable machine learning predictor called PSILC was developed and successfully validated for predicting overall and metastasis-free survival in ILC. Integration of PSILC with CRISPR-Cas9 screening data from breast cancer cell lines revealed 16 candidate therapeutic targets that were synthetic lethal with high-risk ILCs. This study provides interpretable prognostic and predictive biomarkers of ILC which could serve as the starting points for targeted drug discovery for this disease.

Canonical Kaiso target genes define a functional signature that associates with breast cancer survival and the invasive lobular carcinoma histological type

Invasive lobular carcinoma (ILC) is a low- to intermediate-grade histological breast cancer type caused by mutational inactivation of E-cadherin function, resulting in the acquisition of anchorage independence (anoikis resistance). Most ILC cases express estrogen receptors, but options are limited in relapsed endocrine-refractory disease as ILC tends to be less responsive to standard chemotherapy. Moreover, ILC can relapse after >15 years, an event that currently cannot be predicted. E-cadherin inactivation leads to p120-catenin-dependent relief of the transcriptional repressor Kaiso (ZBTB33) and activation of canonical Kaiso target genes. Here, we examined whether an anchorage-independent and ILC-specific transcriptional program correlated with clinical parameters in breast cancer. Based on the presence of a canonical Kaiso-binding consensus sequence (cKBS) in the promoters of genes that are upregulated under anchorage-independent conditions, we defined an ILC-specific anoikis resistance transcriptome (ART). Converting the ART genes into human orthologs and adding published Kaiso target genes resulted in the Kaiso-specific ART (KART) 33-gene signature, used subsequently to study correlations with histological and clinical variables in primary breast cancer. Using publicly available data for ERPOS Her2NEG breast cancer, we found that expression of KART was positively associated with the histological ILC breast cancer type (p < 2.7E-07). KART expression associated with younger patients in all invasive breast cancers and smaller tumors in invasive ductal carcinoma of no special type (IDC-NST) (<2 cm, p < 6.3E-10). We observed associations with favorable long-term prognosis in both ILC (hazard ratio [HR] = 0.51, 95% CI = 0.29-0.91, p < 3.4E-02) and IDC-NST (HR = 0.79, 95% CI = 0.66-0.93, p < 1.2E-04). Our analysis thus defines a new mRNA expression signature for human breast cancer based on canonical Kaiso target genes that are upregulated in E-cadherin deficient ILC. The KART signature may enable a deeper understanding of ILC biology and etiology. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Lobular Carcinoma of the Breast: A Comprehensive Review with Translational Insights

The second most common breast carcinoma, invasive lobular carcinoma, accounts for approximately 15% of tumors of breast origin. Its incidence has increased in recent times due in part to hormone replacement therapy and improvement in diagnostic modalities. Although believed to arise from the same cell type as their ductal counterpart, invasive lobular carcinomas (ILCs) are a distinct entity with different regulating genetic pathways, characteristic histologies, and different biology. The features most unique to lobular carcinomas include loss of E-Cadherin leading to discohesion and formation of a characteristic single file pattern on histology. Because most of these tumors exhibit estrogen receptor positivity and Her2 neu negativity, endocrine therapy has predominated to treat these tumors. However novel treatments like CDK4/6 inhibitors have shown importance and antibody drug conjugates may be instrumental considering newer categories of Her 2 Low breast tumors. In this narrative review, we explore multiple pathological aspects and translational features of this unique entity. In addition, due to advancement in technologies like spatial transcriptomics and other hi-plex technologies, we have tried to enlist upon the characteristics of the tumor microenvironment and the latest associated findings to better understand the new prospective therapeutic options in the current era of personalized treatment.

Association between PIK3CA activating mutations and outcomes in early-stage invasive lobular breast carcinoma treated with adjuvant systemic therapy

BACKGROUND

The aim of the study was to evaluate the independent prognostic role of PIK3CA activating mutations and an association between PIK3CA activating mutations and efficacy of adjuvant endocrine therapy (ET) in patients with operable invasive lobular carcinoma (ILC).

PATIENTS AND METHODS

A single institution study of patients with early-stage ILC treated between 2003 and 2008 was performed. Clinicopathological parameters, systemic therapy exposure and outcomes (distant metastasis-free survival [DMFS] and overall survival [OS]) were collected based on presence or absence of PIK3CA activating mutation in the primary tumor determined using a quantitative polymerase chain reaction (PCR)-based assay. An association between PIK3CA mutation status and prognosis in all patient cohort was analyzed by Kaplan-Meier survival analysis, whereas an association between PIK3CA mutation and ET was analyzed in estrogen receptors (ER) and/or progesterone receptors (PR)-positive group of our patients by the Cox proportional hazards model.

RESULTS

Median age at diagnosis of all patients was 62.8 years and median follow-up time was 10.8 years. Among 365 patients, PIK3CA activating mutations were identified in 45%. PIK3CA activating mutations were not associated with differential DMFS and OS (p = 0.36 and p = 0.42, respectively). In patients with PIK3CA mutation each year of tamoxifen (TAM) or aromatase inhibitor (AI) decreased the risk of death by 27% and 21% in comparison to no ET, respectively. The type and duration of ET did not have significant impact on DMFS, however longer duration of ET had a favourable impact on OS.

CONCLUSIONS

PIK3CA activating mutations are not associated with an impact on DMFS and OS in early-stage ILC. Patients with PIK3CA mutation had a statistically significantly decreased risk of death irrespective of whether they received TAM or an AI.

Genomic assays for lobular breast carcinoma

BACKGROUND

One of the current challenges in breast cancer is the appropriate treatment of invasive lobular breast cancer (ILC) and defining the high-risk group within ILC. The biological character of ILC typically translates to a good prognosis, however, several studies have indicated that the long-term prognosis is worse than for patients diagnosed with the more commonly invasive ductal carcinoma. Many genomic tests are now available to determine whether those patients are at high risk (HR) and enable tailored treatment. Unfortunately, most of the studies in which these genomic tests have been evaluated entail retrospective analysis of a prospective trial.

AIM

This review focuses on the validation of the available genomic assays based on trials performed in ILC patients, where in some instances, the various subtypes of ILC (classical, pleomorphic, and non-classic type) were taken into account.

RESULTS

Using Oncotype DX in retrospective studies, only 1.3%-8% of ILC tumors were categorized as HR tumors. For MammaPrint, 24% of patients were classified as HR, which was associated with poor outcome. In a recent sub-analysis of the MINDACT study comprising 487 ILC patients, 16.2% were high genomic risk. EndoPredict, Prosigna Breast Cancer Prognostic Gene Signature Assay, and the Breast Cancer Index have been validated in patients receiving only endocrine treatment.

CONCLUSION

Although ILC accounts for the second most common breast cancer subtype in women, none of these tests encompass tumor morphology in their algorithms. Prospective studies on ILC with genomic assays are warranted given the various subtypes of and treatment options for this underestimated, but frequently occurring cancer.

RELEVANCE FOR PATIENTS

Genomic assays can be employed in ILC patients to predict the risk of recurrence and identify those patients who might benefit from chemotherapy in addition to their standard treatment regimen.

Clinicopathological Features and Outcomes Comparing Patients With Invasive Ductal and Lobular Breast Cancer

BACKGROUND

There is increasing interest in better understanding the biology and clinical presentation of invasive lobular cancer (ILC), which is the most common special histological subtype of breast cancer. Limited large contemporary data sets are available allowing comparison of clinicopathologic features between ILC and invasive ductal cancer (IDC).

METHODS

The Great Lakes Breast Cancer Consortium was formed to compare clinical behavior of ILC (n = 3617) and IDC (n = 30 045) from 33 662 patients treated between 1990 and 2017 at 3 large clinical centers. We used Kaplan-Meier analysis, Cox proportional hazards modeling, and propensity score matching to evaluate treatment differences and outcomes. All statistical testing used 2-sided P values.

RESULTS

Compared with IDC, patients with ILC were more frequently diagnosed at later stages and with more lymph node involvement (corrected P < .001). Estrogen receptor-positive ILCs were of lower grade (grade 1 and 2: 90% in ILC vs 72% in IDC) but larger in size (T3 and 4: 14.3% in ILC vs 3.4% in IDC) (corrected P < .001), and since 1990, the mean ILC size detected at diagnosis increased yearly. Patients with estrogen receptor (ER)-positive ILC underwent statistically significantly more mastectomies compared with ER-positive IDC (57% vs 46%). Using Kaplan-Meier analysis, patients with ER-positive ILC had statistically significantly worse disease-free survival and overall survival than ER-positive IDC although 6 times more IDCs were classified as high risk by OncotypeDx Breast Recurrence Score assay.

CONCLUSIONS

This large, retrospective, collaborative analysis with 3 clinical centers identified meaningful differences in clinicopathological features between ILC and IDC, providing further evidence that these are 2 different entities requiring different clinical management.

Circulating tumour DNA characterisation of invasive lobular carcinoma in patients with metastatic breast cancer

BACKGROUND

Limited data exist to characterise molecular differences in circulating tumour DNA (ctDNA) for patients with invasive lobular carcinoma (ILC). We analysed metastatic breast cancer patients with ctDNA testing to assess genomic differences among patients with ILC, invasive ductal carcinoma (IDC), and mixed histology.

METHODS

We retrospectively analysed 980 clinically annotated patients (121 ILC, 792 IDC, and 67 mixed histology) from three academic centers with ctDNA evaluation by Guardant360™. Single nucleotide variations (SNVs), copy number variations (CNVs), and oncogenic pathways were compared across histologies.

FINDINGS

ILC was significantly associated with HR+ HER2 negative and HER2 low. SNVs were higher in patients with ILC compared to IDC or mixed histology (Mann Whitney U test, P < 0.05). In multivariable analysis, HR+ HER2 negative ILC was significantly associated with mutations in CDH1 (odds ratio (OR) 9.4, [95% CI 3.3-27.2]), ERBB2 (OR 3.6, [95% confidence interval (CI) 1.6-8.2]), and PTEN (OR 2.5, [95% CI 1.05-5.8]) genes. CDH1 mutations were not present in the mixed histology cohort. Mutations in the PI3K pathway genes (OR 1.76 95% CI [1.18-2.64]) were more common in patients with ILC. In an independent cohort of nearly 7000 metastatic breast cancer patients, CDH1 was significantly co-mutated with targetable alterations (PIK3CA, ERBB2) and mutations associated with endocrine resistance (ARID1A, NF1, RB1, ESR1, FGFR2) (Benjamini-Hochberg Procedure, all q < 0.05).

INTERPRETATION

Evaluation of ctDNA revealed differences in pathogenic alterations and oncogenic pathways across breast cancer histologies with implications for histologic classification and precision medicine treatment.

FUNDING

Lynn Sage Cancer Research Foundation, OncoSET Precision Medicine Program, and UL1TR001422.

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

BACKGROUND

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

DESIGN

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

RESULTS

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

CONCLUSION

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

The 21-Gene Recurrence Score in Clinically High-Risk Lobular and Ductal Breast Cancer: A National Cancer Database Study

Objective

The aim of this study was to evaluate whether patients with invasive lobular carcinoma (ILC) are more likely to have discordant clinical and genomic risk than those with invasive ductal carcinoma (IDC) when using the 21-gene recurrence score (RS), and to assess overall survival outcomes of patients with 1–3 positive nodes and RS ≤25 with and without chemotherapy, stratified by histology.

Methods

We performed a cohort study using the National Cancer Database and included patients with hormone receptor-positive, HER2-negative, stage I–III invasive breast cancer who underwent 21-gene RS testing. Our primary outcome was rate of discordant clinical and genomic risk status by histologic subtype. Propensity score matching was used to compare 60-month overall survival in individuals with 1–3 positive nodes and RS ≤25 who did and did not receive chemotherapy.

Results

Overall, 186,867 patients were included in our analysis, including 37,685 (20.2%) patients with ILC. There was a significantly higher rate of discordant clinical and genomic risk in patients with ILC compared with IDC. Among patients with 1–3 positive nodes and RS ≤25, there was no significant difference in survival between those who did and did not receive chemotherapy in the IDC or ILC cohorts. Unadjusted exploratory analyses of patients under age 50 years with 1–3 positive nodes and RS ≤25 showed improved overall survival in IDC patients who received chemotherapy, but not among those with ILC.

Conclusion

Our findings highlight the importance of lobular-specific tools for stratifying clinical and genomic risk, as well as the need for histologic subtype-specific analyses in randomized trials.

Supplementary Information

The online version contains supplementary material available at 10.1245/s10434-022-12065-3.

Multi-omics analyses provide novel biological insights to distinguish lobular ductal types of invasive breast cancers

BACKGROUND

Invasive lobular carcinoma (ILC) treatment is similar to invasive ductal carcinoma (IDC; now invasive carcinoma-no special type, IBC-NST), based on its intrinsic subtype. However, further investigation is required for an integrative understanding of differentially perturbed molecular patterns and pathways in these histotypes.

METHODS

A dataset of 780 IDC and 201 ILC samples from the TCGA-BRCA project for cross-platform multi-omics was analyzed. We leveraged a consensus approach integrating different bioinformatic algorithms to analyze mutations, CNAs, mRNA, miRNA abundance, methylation, and protein abundance to understand the complex crosstalks that distinguish ILC and IDC samples. A histotype-matched comparison was performed. We performed Cox survival analyses for prognosis based on our identified 53 histotype-specific and four discordant genes.

RESULTS

Approximately 90% of ILC cases were of the luminal subtype. Somatic mutations in CDH1 were higher in ILC than in IDC (FDR-adjusted p < 0.01). Fifty-three significant oncogenic or tumor-suppressive DEGs were identified in a single histotype. PPAR signaling and lipolysis regulation in adipocytes were significantly enriched in ILC tumors. CDH1 protein had the highest differential abundance (AUC: 0.85). Moreover, BTG2, GSTA2, GPR37L1, and PGBD5 amplification was associated with poorer OS in ILC compared with no alteration. RIMS2, NACA4P, MYC, ZFPM2, and POU5F1B amplification showed a lower overall survival in patients with IDC. miR-195 showed an IDC-specific downregulation, causing overexpression of CCNE1. Integrative multi-omics supervised analysis identified 296 differentially expressed genes that successfully distinguished IDC and ILC histotypes.

CONCLUSIONS

Our findings identify novel molecular candidates that potentially drive and modify the disease differentially among these histotypes.

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

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

The 21-gene recurrence score in early non-ductal breast cancer: a National Cancer Database analysis

The 21-gene recurrence score (RS) is prognostic for recurrence and predictive of chemotherapy benefit in early estrogen receptor-positive (ER +) HER2-negative (HER2-) breast cancer (BCA). We evaluated clinicopathologic characteristics, RS and chemotherapy benefit in invasive ductal carcinoma (IDC), invasive lobular carcinoma (ILC), and carcinomas of mixed histologies (ductal + lobular (DLC), ductal + other (DOC), lobular + other (LOC)). Women diagnosed between 1/1/2010 and 1/1/2014 with ER + HER2- BCA, measuring <5 cm, with 0–3 involved axillary nodes, surgery as first treatment, and available RS, were identified from the NCDB. Associations between categorical variables were examined using chi-square test. Cox proportional hazards model was used to examine overall survival (OS) differences among histology subtypes. IDC was associated with smaller size, high grade, and RS > 26. ILC was associated with larger size, and least likely to be high grade (p < 0.0001). Lobular histology was associated with lower incidence of RS > 26. IDC patients (pts) were more likely to receive chemotherapy than pts with other histologies (p < 0.0001). OS for IDC, ILC and DOC were similar. DLC was associated with improved OS (HR 0.82, p = 0.02). Adjuvant chemotherapy was associated with improved OS in IDC (HR = 0.76, p < 0.0001) but not in ILC (HR = 0.99, p = 0.93), DLC (HR = 1.04, p = 0.86), DOC (HR = 0.87, p = 0.71), or LOC (HR = 2.91, p = 0.10). Lobular and mixed BCA histologies have distinct clinicopathologic features compared with IDC, and are less likely to have high RS. OS is similar for IDC and ILC. Although chemotherapy benefit was seen only in IDC, benefit for ILC with RS > 26 cannot be excluded.

Prognostic Utility of Breast Cancer Index to Stratify Distant Recurrence Risk in Invasive Lobular Carcinoma

PURPOSE

The prognostic utility of Breast Cancer Index (BCI) for risk assessment of overall (0-10 years), early (0-5 years), and late (5-10 years) distant recurrence (DR) in hormone receptor-positive (HR+) invasive lobular carcinoma (ILC) was evaluated.

EXPERIMENTAL DESIGN

BCI gene expression analysis was performed blinded to clinical outcome utilizing tumor specimens from patients with HR+ ILC from a multi-institutional cohort. The primary endpoint was time to DR. Kaplan-Meier analyses of overall, early, and late DR risk were performed, and statistical significance was evaluated by log-rank test and Cox proportional hazards regression. The prognostic contribution of BCI in addition to clinicopathologic factors was evaluated by likelihood ratio analysis.

RESULTS

Analysis of 307 patients (99% ER+, 53% T1, 42% N+, 70% grade II) showed significant differences in DR over 10 years based on BCI risk categories. BCI low- and intermediate-risk patients demonstrated similar DR rates of 7.6% and 8.0%, respectively, compared with 27.0% for BCI high-risk patients. BCI was a significant independent prognostic factor for overall 10-year DR [HR = 4.09; 95% confidence interval (CI), 2.00-8.34; P = 0.0001] as well as for both early (HR = 8.19; 95% CI, 1.85-36.30; P = 0.0042) and late (HR = 3.04; 95% CI, 1.32-7.00; P = 0.0224) DR. In multivariate analysis, BCI remained the only statistically significant prognostic factor for DR (HR = 3.49; 95% CI, 1.28-9.54; P = 0.0150).

CONCLUSIONS

BCI is an independent prognostic factor for ILC and significantly stratified patients for cumulative risk of 10-year, early, and late DR. BCI added prognostic value beyond clinicopathologic characteristics in this distinct subtype of breast cancer.

How Researchers, Clinicians and Patient Advocates Can Accelerate Lobular Breast Cancer Research

Simple Summary

This commentary reflects a collaborative effort between international Invasive Lobular Carcinoma (ILC)-focused breast cancer researchers, clinicians and patient advocate leaders. It offers a perspective on the progress made in ILC research in recent years and discusses the recent rise in patient advocate involvement to advance ILC research, raise awareness and educate about this disease. It outlines several distinct challenges in conducting ILC research and describes opportunities and suggestions for ways researchers, clinicians and advocates can work together to advance ILC research to develop new therapies and refine the care offered to patients.

Abstract

Breast cancer research and therapies have significantly advanced in recent years. However, Invasive Lobular Carcinoma (ILC), the second most common histological type of breast cancer and the sixth most frequently diagnosed cancer of women, has not always benefited from critical analysis, missing opportunities to better understand this important subtype. Recent progress understanding the biological and behavioral differences of ILC demonstrates that it is a unique subtype of breast cancer which can respond differently to common therapies. These new insights have increased interest in researching lobular breast disease. Concurrently, the formation of motivated patient-led advocacy organizations working in partnership with basic, translational and clinical researchers creates new opportunities, including connecting a dispersed patient population to research, encouraging new research funding and connecting patient advocates to researchers to advance common goals. This commentary will explore the unprecedented opportunity to drive multidisciplinary, multicenter and international collaborative research into lobular breast cancer that builds on recent research progress. Collaborative research partnerships that include advocates can result in a better understanding of ILC, identify targeted therapies and refine standard of care therapies that are currently equally applied to all breast cancers, resulting in improvements in the diagnosis, treatment and follow-up care for patients with ILC.

The Genomic Landscape of Lobular Breast Cancer

Invasive lobular carcinoma (ILC) is the second most common breast cancer histologic subtype, accounting for approximately 15% of all breast cancers. It is only recently that its unique biology has been assessed in high resolution. Here, we present a meta-analysis of ILC sequencing datasets, to provide a long-awaited ILC-specific resource, and to confirm the prognostic value and strength of association between a number of clinico-pathology features and genomics in this special tumour type. We consider panel (n = 684), whole exome (n = 215) and whole genome sequencing data (n = 48), and review histology of The Cancer Genome Atlas cases to assign grades and determine whether the ILC is of classic type or a variant, such as pleomorphic, prior to performing statistical analyses. We demonstrate evidence of considerable genomic heterogeneity underlying a broadly homogeneous tumour type (typically grade 2, estrogen receptor (ER)-positive); with genomes exhibiting few somatic mutations or structural alterations, genomes with a hypermutator phenotype, and tumours with highly rearranged genomes. We show that while CDH1 (E-cadherin) and PIK3CA mutations do not significantly impact survival, overall survival is significantly poorer for patients with a higher tumour mutation burden; this is also true for grade 3 tumours, and those carrying a somatic TP53 mutation (and these cases were more likely to be ER-negative). Taken together, we have compiled a meta-dataset of ILC with molecular profiling, and our analyses show that the genomic landscape significantly impacts the tumour's variable natural history and overall survival of ILC patients.

Invasive Lobular Carcinoma of the Breast: Ongoing Trials, Challenges, and Future Directions

Purpose of Review

Invasive lobular carcinoma (ILC) is increasingly recognized as a distinct subtype of breast cancer with unique management challenges. We reviewed currently available clinical trials for patients with ILC.

Recent Findings

We describe the rationale for and study design of clinical trials for patients with both early stage and metastatic ILC. Molecular alterations specific to or enriched in ILC may serve as treatment targets.

Summary

ILC has specific features that may be treatment targets. Clinical trials for ILC are available and being developed.

Comprehensive Review of Molecular Mechanisms and Clinical Features of Invasive Lobular Cancer

Invasive lobular carcinoma (ILC) accounts for 10% to 15% of breast cancers in the United States, 80% of which are estrogen receptor (ER)-positive, with an unusual metastatic pattern of spread to sites such as the serosa, meninges, and ovaries, among others. Lobular cancer presents significant challenges in detection and clinical management given its multifocality and multicentricity at presentation. Despite the unique features of ILC, it is often lumped with hormone receptor-positive invasive ductal cancers (IDC); consequently, ILC screening, treatment, and follow-up strategies are largely based on data from IDC. Despite both being treated as ER-positive breast cancer, querying the Cancer Genome Atlas database shows distinctive molecular aberrations in ILC compared with IDC, such as E-cadherin loss (66% vs. 3%), FOXA1 mutations (7% vs. 2%), and GATA3 mutations (5% vs. 20%). Moreover, compared with patients with IDC, patients with ILC are less likely to undergo breast-conserving surgery, with lower rates of complete response following therapy as these tumors are less chemosensitive. Taken together, this suggests that ILC is biologically distinct, which may influence tumorigenesis and therapeutic strategies. Long-term survival and clinical outcomes in patients with ILC are worse than in stage- and grade-matched patients with IDC; therefore, nuanced criteria are needed to better define treatment goals and protocols tailored to ILC's unique biology. This comprehensive review highlights the histologic and clinicopathologic features that distinguish ILC from IDC, with an in-depth discussion of ILC's molecular alterations and biomarkers, clinical trials and treatment strategies, and future targets for therapy. IMPLICATIONS FOR PRACTICE: The majority of invasive lobular breast cancers (ILCs) are hormone receptor (HR)-positive and low grade. Clinically, ILC is treated similar to HR-positive invasive ductal cancer (IDC). However, ILC differs distinctly from IDC in its clinicopathologic characteristics and molecular alterations. ILC also differs in response to systemic therapy, with studies showing ILC as less sensitive to chemotherapy. Patients with ILC have worse clinical outcomes with late recurrences. Despite these differences, clinical trials treat HR-positive breast cancers as a single disease, and there is an unmet need for studies addressing the unique challenges faced by patients diagnosed with ILC.

Invasive lobular carcinoma of the breast: the increasing importance of this special subtype

Invasive lobular carcinoma (ILC) is the most common of the breast cancer special types, accounting for up to 15% of all breast cancer cases. ILCs are noted for their lack of E-cadherin function, which underpins their characteristic discohesive growth pattern, with cells arranged in single file and dispersed throughout the stroma. Typically, tumours are luminal in molecular subtype, being oestrogen and progesterone receptor positive, and HER2 negative. Since last reviewing the lobular literature (McCart Reed et al., Breast Cancer Res 17:12, 2015), there has been a considerable increase in research output focused on this tumour type, including studies into the pathology and management of disease, a high-resolution definition of the genomic landscape of tumours as well as the evolution of several potential therapeutic avenues. There abounds a huge amount of new data, which we will review herein.

Differential impact of prognostic parameters in hormone receptor-positive lobular breast cancer

BACKGROUND

Invasive lobular breast cancer (BC) is the second most common BC subtype. Prognostic parameters (tumor classification, lymph node status, histologic grade, Oncotype DX recurrence score [RS], progesterone receptor status, and Ki67 index) were retrospectively studied in a large, prospective clinical trial encompassing 2585 patients who had hormone receptor-positive early BC (the West German Study Group PlanB trial).

METHODS

BCs were centrally reviewed and classified as lobular (n = 353; 14%) or nonlobular (n = 2232; 86%). The median follow-up was 60 months. Five-year disease-free survival (DFS) estimates were obtained using the Kaplan-Meier method. Prognostic parameters were evaluated using Cox proportional hazard models.

RESULTS

Lobular BC was associated with higher tumor classification, higher lymph node status, lower histologic grade, lower Ki67 index, and low or intermediate RS. The prevalence of high RS (RS range, 26-100) was 3-fold lower in patients who had lobular BC compared with those who had nonlobular BC (8% vs 24%; P < .001). However, 5-year DFS estimates for lobular and nonlobular BC were similar (92.1% and 92.3%, respectively; P = .673). In multivariate analyses, prognostic parameters for DFS in lobular BC included grade 3 (hazard ratio, 5.06; 95% CI, 1.91-13.39) and a pathologic lymph node status (pN) of pN3 (hazard ratio, 12.16; 95% CI, 3.87-38.24), but not RS. By contrast, prognostic parameters in nonlobular BC included grade 3 (hazard ratio, 1.65; 95% CI, 1.11-2.44), pN3 (hazard ratio, 3.68; 95% CI, 1.60-8.46), and high RS (hazard ratio, 2.49; 95% CI, 1.69-3.68).

CONCLUSIONS

Lobular BC is associated with low and intermediate RS, although 5-year DFS is similar to that of nonlobular BC. The effect of the RS in lobular BC appears to be distinct from that in nonlobular BC. For risk assessment, the RS needs to be complemented by clinicopathologic parameters for therapy decision making.

Genetic analysis of pleomorphic and florid lobular carcinoma in situ variants: frequent ERBB2/ERBB3 alterations and clonal relationship to classic lobular carcinoma in situ and invasive lobular carcinoma

Pleomorphic (PLCIS) and florid (FLCIS) lobular carcinoma in situ are rare histologic variants of LCIS that are considered more aggressive than classic LCIS (CLCIS), but optimal treatment is controversial. The genetic drivers of these lesions and their clonal relationships to paired CLCIS and ILC have not been characterized. We used capture-based next-generation sequencing to profile 16 LCIS variants (ten PLCIS, six FLCIS), including paired synchronous ILC and CLCIS in 11 and nine cases, respectively. Recurrent pathogenic alterations included CDH1 (9/10 PLCIS, 6/6 FLCIS), PIK3CA (7/10 PLCIS, 2/6 FLCIS), ERBB2 (6/10 PLCIS, 2/6 FLCIS; six mutations, two amplifications), ERBB3 (1/10 PLCIS, 2/6 FLCIS), FOXA1 (4/10 PLCIS, 1/6 FLCIS), TP53 (3/10 PLCIS), and CCND1 (2/10 PLCIS, 1/6 FLCIS). Mutational profiles and mean copy number alterations (CNA) were similar between LCIS variants with and without ILC. Compared with ILC in The Cancer Genome Atlas (TCGA), PLCIS, FLCIS, and associated ILC were enriched for ERBB2 mutations, and PLCIS was enriched for TP53 and FOXA1 mutations. Shared pathogenic mutations and CNA were identified between the LCIS variant and ILC in all cases, and between CLCIS and the LCIS variant/ILC in 89%. CLCIS to PLCIS progression was associated with increased mean nonsynonymous mutations and additional pathogenic alterations and/or CNA in 80%. Mean nonsynonymous mutations and CNA were similar between PLCIS and ILC, although additional pathogenic mutations were associated with invasion in a subset (43%). FLCIS harbored additional clonal pathogenic mutations in only 1/3 cases, and these were not shared with ILC, which was genetically divergent. In another case, ILC was genetically more similar to CLCIS than FLCIS. The results highlight clonal relationships between PLCIS/FLCIS and CLCIS, and implicate PLCIS as a genetically advanced ILC precursor. Frequent ERBB2/ERBB3 alterations in PLCIS and FLCIS are consistent with more aggressive behavior and may have prognostic and therapeutic implications.

Breast Cancer: A Molecularly Heterogenous Disease Needing Subtype-Specific Treatments

Breast cancer is the most commonly occurring cancer in women. There were over two-million new cases in world in 2018. It is the second leading cause of death from cancer in western countries. At the molecular level, breast cancer is a heterogeneous disease, which is characterized by high genomic instability evidenced by somatic gene mutations, copy number alterations, and chromosome structural rearrangements. The genomic instability is caused by defects in DNA damage repair, transcription, DNA replication, telomere maintenance and mitotic chromosome segregation. According to molecular features, breast cancers are subdivided in subtypes, according to activation of hormone receptors (estrogen receptor and progesterone receptor), of human epidermal growth factors receptor 2 (HER2), and or BRCA mutations. In-depth analyses of the molecular features of primary and metastatic breast cancer have shown the great heterogeneity of genetic alterations and their clonal evolution during disease development. These studies have contributed to identify a repertoire of numerous disease-causing genes that are altered through different mutational processes. While early-stage breast cancer is a curable disease in about 70% of patients, advanced breast cancer is largely incurable. However, molecular studies have contributed to develop new therapeutic approaches targeting HER2, CDK4/6, PI3K, or involving poly(ADP-ribose) polymerase inhibitors for BRCA mutation carriers and immunotherapy.

Transcriptional Signature Derived from Murine Tumor-Associated Macrophages Correlates with Poor Outcome in Breast Cancer Patients

Tumor-associated macrophages (TAMs) are frequently the most abundant immune cells in cancers and are associated with poor survival. Here, we generated TAM molecular signatures from K14cre;Cdh1flox/flox;Trp53flox/flox (KEP) and MMTV-NeuT (NeuT) transgenic mice that resemble human invasive lobular carcinoma (ILC) and HER2+ tumors, respectively. Determination of TAM-specific signatures requires comparison with healthy mammary tissue macrophages to avoid overestimation of gene expression differences. TAMs from the two models feature a distinct transcriptomic profile, suggesting that the cancer subtype dictates their phenotype. The KEP-derived signature reliably correlates with poor overall survival in ILC but not in triple-negative breast cancer patients, indicating that translation of murine TAM signatures to patients is cancer subtype dependent. Collectively, we show that a transgenic mouse tumor model can yield a TAM signature relevant for human breast cancer outcome prognosis and provide a generalizable strategy for determining and applying immune cell signatures provided the murine model reflects the human disease.