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

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

Rapid autopsies to enhance metastatic research: the UPTIDER post-mortem tissue donation program

Research on metastatic cancer has been hampered by limited sample availability. Here we present the breast cancer post-mortem tissue donation program UPTIDER and show how it enabled sampling of a median of 31 (range: 5-90) metastases and 5-8 liquids per patient from its first 20 patients. In a dedicated experiment, we show the mild impact of increasing time after death on RNA quality, transcriptional profiles and immunohistochemical staining in tumor tissue samples. We show that this impact can be counteracted by organ cooling. We successfully generated ex vivo models from tissue and liquid biopsies from distinct histological subtypes of breast cancer. We anticipate these and future findings of UPTIDER to elucidate mechanisms of disease progression and treatment resistance and to provide tools for the exploration of precision medicine strategies in the metastatic setting.

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

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

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

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

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

PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

Obesity-associated changes in molecular biology of primary breast cancer

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

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

INTRODUCTION

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Abstract P6-05-10: An international survey on invasive lobular breast cancer (ILC) reveals gaps in knowledge and top priority research areas

Background: There is growing awareness of the unique etiology, biology, clinical presentation and progression of Invasive lobular breast cancer (ILC), but additional research is needed to assure translation of findings into management and treatment guidelines. We performed a survey to: 1) analyze the landscape of the current understanding of ILC, and 2) identify consensus research questions on ILC.

Methods: The IRB-approved survey was developed with input from representatives of three major stakeholder groups - breast cancer clinicians/researchers, laboratory-based researchers, and advocates/patients. We fielded the survey from March to May 2022 using targeted email and via social media.

Results: 1,774 participants answered at least one question and 1,310 finished the survey. Participants are from 66 countries from all continents (except Antarctica). Respondents self-identified as clinicians (mostly medical oncologists and surgeons) (N=413), researchers (N=376), and breast cancer patients (1,121), with some belonging to more than one category. 26% of the patients who participated in the survey belong to advocate groups.

Only 46% of clinicians reported being confident in describing the differences between ILC and no special type (NST) (invasive ductal) breast cancer. Knowledge of histology was seen as important (73%), affecting their treatment decisions (51%), and refined treatment guidelines would be valuable for patients with ILC in the future (76%). 85% of clinicians have never powered a clinical trial to allow subset analysis for histological subtypes, but the majority would consider it. 88% would participate in a consortium to conduct clinical trials on ILC. The top two most important research questions were: 1) determining mechanisms of endocrine resistance, and, 2) identifying novel therapeutic targets, repurposing existing drugs and progressing them to clinical trials.

Of the researchers, 48% reported being confident in describing differences between ILC and NST. They reported that ILCs are inadequately presented in large genomic data sets (52%), and that ILC models are insufficient (42%). Only 13% of respondents have inadequate access to tissue or blood from patients with ILC. The top two most important research questions identified by the laboratory researchers overlapped with those identified by the clinicians, i.e. understanding of endocrine resistance and identifying novel drugs that can be tested in clinical trials.

The majority of patients (52%) thought that their health care providers did not explain unique features of ILC, and that in general communication was limited. When asked about top research question, they chose: 1) Improvement of ILC screening/early detection, and, 2) Identifying new and specific imaging tools for ILC.

When comparing top priority topics across six research domains, there was a high degree of consistency, especially among clinicians and researcher, but less so when compared with the breast cancer patients (Table 1).

Conclusion: In summary, we have gathered timely and representative information from an international community of clinicians, researchers, and patients/advocates that we expect will lay the foundation for a community-informed collaborative research agenda, with the goal of improving the management and personalizing treatment for patients with ILC.

Table 1. Ratings by all three stakeholder groups of the most critical and impactful ILC research topics. Top box scores between stakeholder groups were compared using chi-square analysis.

Citation Format: Steffi Oesterreich, Leigh Pate, ADRIAN V. LEE, Rachel C. Jankowitz, Patrick Derksen, Rita Mukhtar, Otto Metzger, Matthew J. Sikora, Christopher Li, Christos Sotiriou, Gary Ulaner, Jorge Reis-Filho, Nancy E Davidson, Karen Van Baelen, Laurie Hutcheson, Siobhan Freeney, Flora Migyanka, Claire Turner, Todd Bear, Christine Desmedt. An international survey on invasive lobular breast cancer (ILC) reveals gaps in knowledge and top priority research areas [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-05-10.

Abstract P5-14-01: Transcriptomic insights into lobular breast cancer biology: a retrospective analysis of the MINDACT clinical trial

Background: Invasive lobular carcinoma (ILC) represents the second most common subtype of breast cancer after invasive breast cancer of no special type (NST). In this retrospective analysis of the MINDACT trial, we aimed at identifying/refining the transcriptomic differences between: 1) estrogen receptor positive/HER2-negative (ER+/HER2-) ILC versus ER+/HER2- NST, 2) classic and non-classic ER+/HER2- ILC, and, 3) recurring and non-recurring ER+/HER2- ILC in the subgroup of patients with a low clinical and low genomic (cL/gL) risk (as defined by a modified version of Adjuvant Online! and the 70-gene signature). Patients and methods: Central pathology review was performed for histological subtype, grade and Ki67 (G.V.) for 5929/6693 (88.6%) of the patients included in the MINDACT trial (NCT00433589). Analysis of transcriptomic data adjusted for age and grade was performed using the R/Bioconductor package ‘limma’ to identify differentially expressed genes (DEGs). DEGs having absolute log-fold change (logFC)≥ 0.2 and FDR-adjusted p-value (q-value) &lt; 0.05 were considered. Gene set enrichment analyses (GSEA) of MSigDB hallmark gene sets were performed. Adjusted Cox regression models were used to evaluate the association of these hallmarks with disease free survival (DFS) and distant recurrence free survival (DRFS). Results: After central pathological review, 464 patients with ER+/HER2- ILC and 3798 patients with ER+/HER2- NST were identified. Patients with ILC were significantly older at diagnosis, had larger tumors, less axillary nodal involvement, more grade 2 tumors than patients with NST. At the transcriptomic level, we observed a high number of DEGs between these 2 subgroups, confirming their distinct phenotype. CDH1, the gene coding for E-cadherin, was as expected the most highly overexpressed gene in NST versus ILC. We further observed an increased expression of leptin (LEP), leptin receptor (LEPR), lipoprotein lipase (LPL), and the fatty acid transporter CD36 in ILC. This could suggest that ILC relied on increased lipid uptake thanks to the increased contact of ILC tumor cells with the adipocytes. IGF1 was also overexpressed in ILC versus NST, as a potential consequence of high LEP and high LEPR expression. Differences were also evident with regard to the extracellular matrix (ECM), with many collagens, matrix metalloproteinases (MMPs) and other key enzymes (e.g. LOXL1) being differentially expressed. We confirmed a decreased ER-signaling and increased PI3K/Akt signaling in ILC versus NST. Out of the 464 ER+/HER2- ILC tumors, 253 (55%) were classic ILC and 211 (45%) non-classic ILC. There were more grade 3 tumors, more highly proliferative tumors and more nodal involvement in patients with non-classic versus classic ILC. At the transcriptomic level, differences were subtler than the differences seen above. Still, a significant enrichment of the hallmarks related to cell cycle in the non-classic ILC, and of the hallmarks related to epithelial-to-mesenchymal transition, hypoxia, adipogenesis and IL6/JAK/STAT3 signaling in classic ILC was observed. Finally, 216/464 patients with ER+/HER2- ILC (47%) were assigned to the cL/gL risk group and did not receive chemotherapy. 28/216 of these patients (13%) relapsed (DFS, median FU: 8.7 years). Enrichment of hallmarks related to apoptosis, inflammatory response, hypoxia and oncogenic signaling (PI3K/Akt, Ras, c-Myc) was associated with worse survival. Conclusion: This represents, to the best of our knowledge, the largest set of gene expression data for patients with ILC, issued from a clinical trial where histology was reviewed centrally. These results could be used to personalize treatment for patients with ILC. This project is funded by the Breast Cancer Research Foundation.

Citation Format: Christine Desmedt, Ha-Linh Nguyen, François Richard, Sabine Linn, Otto Metzger, Coralie Poncet, Jelle Wesseling, Florentine Hilbers, Kim Aalders, Mauro Delorenzi, Suzette Delaloge, Jean-Yves Pierga, Etienne Brain, Suzan Vrijaldenhoven, Peter A Neijenhuis, Karen Van Baelen, Marion Maetens, Emiel Rutgers, Martine Piccart, Laura Van ’t Veer, Giuseppe Viale, Fatima Cardoso. Transcriptomic insights into lobular breast cancer biology: a retrospective analysis of the MINDACT clinical trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-14-01.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Table 1: effect of FFTP class by multiparity

Table 2: proportion of ER-negative breast cancer subtype

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

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

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

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

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

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

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

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

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

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

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