Pleomorphic Invasive Lobular Carcinoma Research Articles

Neoadjuvant targeted therapy in early resectable HER2-mutant lobular breast cancer.

TPS630 Background: Invasive lobular carcinoma (ILC) accounts for approximately 10-15% of all breast cancers and is characterized by hormone receptor positivity (HR+), low Ki-67 score, and loss of cell adhesion receptors such as E-cadherin. While these tumors tend to be indolent initially, late recurrences and distant metastasis are common, and ILC has very low rates of pathologic complete response (pCR) to both neoadjuvant chemotherapy and endocrine therapy (ET). HER2 ( ERBB2) mutations are enriched in about 10% of unselected ILC, with some reports showing the prevalence as high as 27% in pleomorphic and higher grade ILCs. HER2 mutations in ILC are associated with ET resistance and a worse prognosis. Neratinib is a HER2 tyrosine kinase inhibitor (TKI) currently FDA-approved for adjuvant treatment of HER2-amplified (HER2+) early-stage breast cancer. It has shown safety and efficacy in combination with ET in metastatic HER2-mutant HR+ breast cancer. We hypothesize that neoadjuvant treatment with neratinib and ET will improve pathologic responses in newly diagnosed HER2-mutant HR+ ILC. Methods: This study (NCT05919108) is an open label multi-site Phase II clinical trial for 30 patients with Stage I-III ILCs and a HER2 activating mutation. Patients will be identified by next generation sequencing (NGS) of the diagnostic biopsy and randomized to 4 weeks of ET +/- neratinib; a biopsy will be done at the end of the lead-in phase. All patients will then receive ET and neratinib for 20 weeks prior to proceeding to surgery. To optimize tolerability, the first cycle of neratinib will include a dose escalation and antidiarrheal prophylaxis. The primary objective of this study will be the pre-operative endocrine prognostic index (PEPI) score, which will be compared to a historical PEPI-0 rate for patients with HR+ breast cancer treated with neoadjuvant ET. Secondary objectives will include pCR, residual cancer burden, and rates of breast conserving surgery. Correlative studies will include biomarkers of tumor cell cycle arrest, apoptosis, HER2 pathway activation, and gene expression on the pre- and on-treatment (4 week) biopsy from the lead-in phase to document molecular synergy between neratinib and ET. Patient-derived organoids from the 4-week biopsies will be established and subjected to single-cell RNA, ATAC seq, and DNA sequencing to study tumor evolution and elucidate epigenetic programs and somatic alterations that allow breast cancer survival despite continuous HER2-directed therapy. This is a first-in-kind, mechanism-based, molecularly targeted combination of a HER2 TKI and ET in HER2-mutant ILC. We posit results from this study may generate a clear signal of clinical activity leading to a randomized phase III trial aimed at incorporating HER2-directed therapies as a treatment for operable, early stage ILC. This signal may also suggest for the first time the added value of NGS in patients with newly diagnosed HR+ breast cancer. Clinical trial information: NCT05919108 .

Abstract PO5-06-14: Genomic Landscape and Clinical Outcomes of Triple-Negative Invasive Lobular Carcinoma

Abstract Background: Triple-negative (TN) invasive lobular carcinoma (ILC) of the breast is a rare entity, comprising roughly 2% of primary ILC. Clinicopathologic studies have shown that TN ILC is associated with more pleomorphism, higher nuclear grade, older patient age, and worse disease-related outcomes compared to estrogen receptor-positive (ER+) ILC. Intrinsic subtyping indicates that TN ILC less frequently expresses basal markers than TN invasive ductal carcinoma (IDC). This prompted investigation of the genomic landscape and clinical management of TN ILC to provide insight into potential therapeutic approaches. Methods: Twenty patients with TN ILC were included in this study. Three patients were treated at a single academic center and underwent comprehensive genomic profiling (CGP) of breast or metastatic tissue; clinicopathologic details were obtained from their electronic health records. Seventeen patients with TN ILC who underwent CGP of breast or metastatic biopsies were included from the Foundation Medicine, Inc. database. PD-L1 testing for all patients was determined by immunohistochemistry (IHC) using the VENTANA SP142 or Dako 22C3 commercial assays. HER2 expression was determined by IHC. Negative HER2 expression was defined as an IHC score of 0, or IHC 1+ or 2+ with non-amplified fluorescence in situ hybridization (FISH). Results: In the Foundation Medicine database of patients with TN ILC, the most frequent genomic alterations were in CDH1 (15/17 patients [88.2%]), TP53 (10/17 patients [58.8%]), and PIK3CA (10/17 patients [58.8%]). Short variant mutations in ERBB2 were found in 3/17 patients (17.6%). Fourteen patients were HER2-low (HER2 IHC 1+ or 2+ with non-amplified FISH). No cases were MSI high or expressed PD-L1 (8 of 17 cases underwent PD-L1 assessment by SP142). Median tumor mutational burden (TMB) was 5 muts/Mb. Among the three patients with TN ILC treated at a single center, the most common somatic mutations were in CDH1 and TP53, and no cases were MSI high or expressed PD-L1 (by SP142 or 22C3). All three patients had pleomorphic ILC, histologic grade 2 or 3, and HER2 IHC 0. One patient with mpT1cN1a(sn) ER+/HER2- ILC of the right breast in 2011 received adjuvant TAC (docetaxel, doxorubicin, cyclophosphamide), breast/axillary radiation, and ten years of adjuvant endocrine therapy. She was diagnosed with TN ILC of the left supraclavicular nodes in 2022; she did not exhibit a response to docetaxel and carboplatin with pembrolizumab, and she subsequently received palliative radiation followed by capecitabine. Another patient with locally advanced TN ILC progressed on the KEYNOTE-522 regimen, immediately developed metastases, and is currently receiving palliative sacituzumab govitecan. The third patient with cT3N1 TN ILC progressed on neoadjuvant therapy (through the I-SPY 2 trial) with oral paclitaxel, encequidar, and dostarlimab, followed by dostarlimab with dose-dense doxorubicin and cyclophosphamide. Her surgical pathology demonstrated ypT3N3a disease with 10 × 7 cm of tumor, and she developed skin metastases on the chest wall within weeks post-operatively. She received comprehensive chest wall and nodal radiation and is currently receiving palliative capecitabine with neratinib given a high variant allele frequency driver somatic ERBB2 mutation. Conclusions: The most common somatic mutations among TN ILC patients included in this study were in CDH1, TP53, and PIK3CA. Currently the management of TN ILC is extrapolated from that of TN IDC, however our patients did not respond to chemoimmunotherapy. The presence of HER2-low status or somatic ERBB2 mutations may provide opportunities for treatment with an anti-HER2 antibody-drug conjugate or tyrosine kinase inhibitor. Studies with larger sample sizes of TN ILC are needed for molecular profiling and assessment of outcomes with specific therapeutic approaches. Citation Format: Hemali Batra-Sharma, Smruthy Sivakumar, Prashanth Ashok Kumar, Ethan Sokol, Rebecca Shatsky, Jeffrey Ross. Genomic Landscape and Clinical Outcomes of Triple-Negative Invasive Lobular Carcinoma [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-06-14.

Abstract CT271: Neoadjuvant targeted therapy in stage I-III HER2-mutant lobular breast cancer

Abstract Background: Invasive lobular carcinoma (ILC) accounts for approximately 10-15% of all breast cancers and is characterized by hormone receptor positivity (HR+), low Ki-67 score, and loss of cell adhesion receptors such as E-cadherin. While these tumors tend to be indolent initially, late recurrences and distant metastasis are common, and ILC has very low rates of pathologic complete response (pCR) to both neoadjuvant chemotherapy and endocrine therapy (ET). HER2 (ERBB2) mutations are enriched in about 10% of unselected ILC, with some reports showing the prevalence as high as 27% in pleomorphic and higher grade ILCs. HER2 mutations in ILC are associated with ET resistance and a worse prognosis. Neratinib is a HER2 tyrosine kinase inhibitor (TKI) currently FDA-approved for adjuvant treatment of HER2-amplified (HER2+) early-stage breast cancer. It has shown safety and efficacy in combination with ET in metastatic HER2-mutant HR+ breast cancer. We hypothesize that neoadjuvant treatment with neratinib and ET will improve pathologic responses in newly diagnosed HER2-mutant HR+ ILC. Methods: This study (NCT05919108) is an open label multi-site Phase II clinical trial for 30 patients with Stage I-III ILCs and a HER2 activating mutation. Patients will be identified by next generation sequencing (NGS) of the diagnostic biopsy and randomized to 4 weeks of ET +/- neratinib; a biopsy will be done at the end of the lead-in phase. All patients will then receive ET and neratinib for 20 weeks prior to proceeding to surgery. To optimize tolerability, the first cycle of neratinib will include a dose escalation and antidiarrheal prophylaxis. The primary objective of this study will be the pre-operative endocrine prognostic index (PEPI) score, which will be compared to a historical PEPI-0 rate for patients with HR+ breast cancer treated with neoadjuvant ET. Secondary objectives will include pCR, residual cancer burden, and rates of breast conserving surgery. Correlative studies will include biomarkers of tumor cell cycle arrest, apoptosis, HER2 pathway activation, and gene expression on the pre- and on-treatment (4 week) biopsy from the lead-in phase to document molecular synergy between neratinib and ET. Patient-derived organoids from the 4-week biopsies will be established and subjected to single-cell RNA, ATAC seq, and DNA sequencing to study tumor evolution and elucidate epigenetic programs and somatic alterations that allow breast cancer survival despite continuous HER2-directed therapy. This is a first in kind, mechanism-based, molecularly targeted combination of a HER2 TKI and ET in HER2-mutant ILC. We posit results from this study may generate a clear signal of clinical activity leading to a randomized Phase III trial aimed at incorporating HER2-directed therapies as a treatment for operable, early stage ILC. This signal may also suggest for the first time the added value of NGS in patients with newly diagnosed HR+ breast cancer. Citation Format: Laura C. Kennedy, Nisha Unni, Ariella B. Hanker, Carlos L. Arteaga. Neoadjuvant targeted therapy in stage I-III HER2-mutant lobular breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT271.

Characteristics of Triple Negative Subtype Breast Cancer in Dr. Hasan Sadikin General Hospital for 5 Years (2019-2023): An Observational Study

Background: Triple-negative breast cancer has a percentage of 15% to 20% in breast cancer patients at the time of first diagnosis. Guidelines from St. Gallen guidelines, the American Society of Clinical Oncology, and the American College of Pathology state that triple-negative breast cancer is breast cancer with ER and PR expression <1%. As an aggressive subtype, outcomes are poor when compared with hormone receptor-positive. Methods: This research is an observational study. The research subjects in this study were triple-negative breast cancer patients in Dr. Hasan Sadikin General Hospital, Surgical Oncology division, West Java, Indonesia, from October 2018 - November 2023. There were 702 research subjects who would be studied. Characteristics of triple-negative breast cancer were taken from medical records. Results: The results showed that the average age of the subjects was 47 years. Based on histology, the most common was Invasive Carcinoma of no special type (86.75%), followed by Invasive lobular carcinoma (7.26%), medullary carcinoma (1.7%), micropapillary carcinoma (0.99%), metaplastic carcinoma (2.36%) and the least amount is Pleomorphic invasive lobular carcinoma (0.71%). The side of the breast affected is not significant, and the highest grade is 3. The involvement of lymph node metastases is due to aggressive tumor subtypes and lymphovascular invasion. Lymphovascular invasion is known to be a negative prognostic factor. It is a late stage for metastasis and local recurrence. Conclusion: Triple-negative breast cancer is breast cancer that has histopathological heterogeneity; most of the tumors are grade 3 and have significant metastases in regional lymph nodes. There is no significant relationship between grading and regional lymph node metastases. there is a significant relationship between lymphovascular invasion and regional lymph nodes metastases.

Expression of PD-L1 in breast invasive lobular carcinoma.

The purpose of this study was to investigate the expression of PD-L1 in invasive lobular carcinoma (ILC) and to determine its implications. Tissue microarrays were constructed for 101 cases of ILC, and immunohistochemical staining for PD-L1 (using 22C3, SP142, and SP263 antibodies) was performed to examine the correlation between staining results and clinicopathologic parameters. The positive cut-off values were defined as tumor cell (TC)≥1%, immune cell (IC)>0%, and IC≥1%. The range of PD-L1 TC positivity was 0.0-2.0%, with PD-L1 SP263 TC showing the highest positivity of 2.0%. The range of PD-L1 IC positivity was 0-21.8% for IC ≥ 1%, with PD-L1 22C3 IC showing the highest positivity. When PD-L1 IC was positive (IC≥1%), the highest antibody agreement was observed between SP263 and SP142 (OA = 93.1%), while the lowest agreement was observed between 22C3 and SP263 (OA = 73.3%, κ = 0.040). PD-L1 22C3 IC positivity (≥1%) was associated with high nuclear grade (p = 0.002), HER-2 positivity (p = 0.019), and pleomorphic type (p = 0.002). PD-L1 expression in ILC shows a low TC positivity rate (0-2%) with various antibody clones and a variable IC positivity rate (0-21.8%). Pleomorphic type ILC exhibits higher PD-L1 IC positivity.

Exploration of cancer associated fibroblasts phenotypes in the tumor microenvironment of classical and pleomorphic Invasive Lobular Carcinoma.

Multiplex immunofluorescence were performed on formalin fixed paraffin embedded tissues using Opal-7 color kit. The antibodies used for phenotyping CAFs were Pan CK (AE1/AE3), CD45, A-SMA, FAP, S100, Thy-1 with optimized dilutions. The images were acquired and analyzed using Vectra 3.0 imaging system and InForm software respectively. We studied 19 different CAFs colocalized phenotypes in the tumor, stroma and overall tissue compartments between classic and pleomorphic ILC. Total A-SMA+, A-SMA+FAP+S100+ and A-SMA+S100+ CAFs demonstrated higher densities in classic ILC cases while FAP+S100+ and S-100+ CAFs were increased in the pleomorphic subtype samples. Our study explores multiple CAFs phenotypes between classical and pleomorphic ILC. We showed that CAFs subset differ between Classic ILC and Pleomorphic ILC. A-SMA CAFs are more prevalent in the TME of classic ILCs whereas Pleomorphic ILCs are dominated by CAFs without A-SMA expression. This also iterates the importance of exploring this particular type of breast carcinoma in more detail, paving the way for meaningful translational research.

Primary Mucinous Cystadenocarcinoma of the Breast Intermixed with Pleomorphic Invasive Lobular Carcinoma: The First Report of This Rare Association.

Primary mucinous cystadenocarcinoma (MCA) is a rare breast carcinoma subtype showing overlapping histopathological features with mucinous cystadenocarcinoma of the ovary and pancreas. Current literature data suggest a favorable prognosis of breast MCAs despite its immunoprofile usually revealing lack of expression of estrogen receptor, progesterone receptor and HER-2 and high Ki67. As far as we know, only 36 cases have been reported in the literature to date. Its ambiguous morpho-phenotypic profile makes histological diagnosis very challenging. It must be distinguished from typical mucin-producing breast carcinomas and, above all, metastases from the same histotype in other sites (ovary, pancreas, appendix). Herein, we report the case of a primary breast MCA occurring in a 41-year-old female with peculiar histological features.

Abstract P2-21-07: Exploring spatial correlations in Breast invasive Lobular Carcinoma subtypes using a novel CAF multiplex immunofluorescence panel

Abstract Background: Recent advances in immunotherapy led to development of new technologies to identify topographical distributions and correlations in the tumor microenvironment, enabling a better understanding of the tumor immune landscape. Based on the 2019 WHO classification Invasive lobular carcinoma (ILC) has various histological presentations. The pleomorphic variant has been reported to be biologically different to the classical counterpart. Cancer associated fibroblasts (CAFs) secrete cytokines and growth factors aiding in tumor growth. CAFs have been shown to express alpha-smooth muscle actin (α-SMA), Thy1, fibroblast activation protein (FAP), S-100. IHC based studies have shown differences in CAFs subpopulation between ILC and IDC. Here, we explored different CAFs subpopulations between Pleomorphic and Classical ILC using multiplex immunofluorescence (mIF). Study design: Multiplex immunofluorescence (mIF) was performed on formalin-fixed paraffin-embedded (FFPE) tissue sections [(n=6, classic ILC; n=6 pleomorphic ILC)] stained with Opal 7-color Kit using an automated system. Sections were stained consecutively with Pancytokeratin, CD45, A-SMA, FAP, S100, Thy-1. Slides were scanned using the Vectra 3.0 spectral imaging system (PerkinElmer). Five tumor ROIs were examined with Phenochart (Akoya/PerkinElmer) viewer and subsequent images were analyzed to explore spatial distances of CK+ cells to the CAFs. Data was generated using InForm and Phenoptr softwares (Akoya Labs) as a median value. Statistical analysis data correlation was performed using SPSS version 24.0 (IBM Corp) Results: Twelve invasive lobular carcinomas cases were evaluated. All cases with classical features were nuclear grade 2 and all pleomorphic cases (n=6) were nuclear grade 3. Six were Luminal B, five were Luminal A and one case was triple negative invasive lobular carcinoma. We studied nineteen different phenotypes of CAFs in the tumor, stroma, and overall tissue compartments. We found statistically significant differences (p-value< 0.05) between the distances of CAFs from the tumor cells in classic and pleomorphic ILC in three phenotypes. The A-SMA+, A-SMA+/S100+ phenotypes were closer to the tumor cells in classic subtype and the S100 only phenotype was closer to the tumor cells in pleomorphic carcinomas. In addition, there were two other phenotypes namely A-SMA+/Thy-1+(closer to tumor cells in classic ILC) and FAP+/S-100+ (closer to tumor cells in pleomorphic ILC), which showed a trend of significance (Table 1) Discussion: TME studies in invasive breast lobular carcinoma have been primarily based on chromogenic IHC. Multiplex immunofluorescence quantifies cell phenotype’s densities and positions in different tissue compartments (tumor vs stroma vs total tissue). Knowing the proximity of an individual TME cells to the tumor cells, aids in pinpointing possible therapeutic targets. Fibroblast dysregulation in cancers, enhances their pro-tumorigenic and anti-tumorigenic potential. Due to their heterogeneity, they can express a wide array of markers. Identifying the full possibility of CAF subsets is one of the keys to discovering actionable targets. Our results showed Alpha- SMA positive, Alpha-SMA/S-100 positive, Alpha SMA/Thy-1 positive CAFs in closer proximity to the classic ILC tumor cells as compared to pleomorphic ILC. Additionally, S-100 positive and FAP/S-100 positive CAFs showed a closer proximity to tumor cells in the pleomorphic subtype. Based on these results we hypothesize that pleomorphic ILCs are closely associated with pro-tumorigenic CAFs as compared to classic ILCs. Larger datasets are needed to confirm this. In conclusion we utilized an objective approach to quantify, phenotype and spatially correlate each cell in the tumor microenvironment. This has helped identifying CAFs subsets that differs in the spatial correlation to tumor cells in ILC subtypes, which can be potential actionable targets. Table 1 Phenotypes of Cancer associated fibroblasts and their statistical correlation between classic vs pleomorphic invasive Lobular carcinomas. Citation Format: Harsh Batra, Renganayaki K. Pandurengan, Heladio P. Ibarguen, Salome A McAllen, Qingqing Ding, Aysegul Sahin, Ignacio Wistuba, Edwin Roger Parra, Maria Gabriela Raso. Exploring spatial correlations in Breast invasive Lobular Carcinoma subtypes using a novel CAF multiplex immunofluorescence panel [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-21-07.

Biomarker profile of invasive lobular carcinoma: pleomorphic versus classic subtypes, clinicopathological characteristics and prognosis analyses.

To compare the clinicopathologic features and prognosis of pleomorphic invasive lobular carcinoma (P-ILC) and classic ILC (C-ILC) according to the biomarker profile. A total of 667 C-ILCs and 133 P-ILCs between 2011 and 2021 were included. Clinicopathologic features and stromal tumor-infiltrating lymphocytes (sTILs) status were evaluated. P-ILCs were divided into subtypes based on ER/PR and HER2 expression. The overall survival and disease-free survival (DFS) of patients were compared among matched P-ILCs, C-ILCs, and invasive ductal carcinomas (IDCs) with biomarker subtypes. Compared to C-ILCs, P-ILCs had greater tumor sizes and stages, fewer ER-positive, more HER2-positive, triple negative (TN), and Ki-67 > 20% tumors (P < 0.05). P-ILCs were subdivided into ER+ (63.1%), HER2+ (21.1%) and TN (15.8%). ER+ P-ILCs were mainlyshowed trabecular and solidgrowth patterns. Apocrine and solid featureswere more strongly associated with HER2+ P-ILCs and TN-P-ILCs, respectively.The prognosis of each biomarker group (ER+, HER2+ and TN) differed by subtype. The P-ILC biomarker subtypes hadworse prognosis than the same subtypes in the IDC group, while there wasno difference between the P-ILC and the C-ILC counterparts. Solid variants of P-ILChad the worst prognosis. Bone was the most common metastatic site in ER+ P-ILCs and TN-P-ILCs. HER2+ P-ILCs tended to metastasize to the brain and liver. DFS of HER2+ P-ILCs and TN-P-ILCs were worse than that of ER+ P-ILCs. Lacking lobular carcinoma in situ and sTILs ≤ 10% were associated with worse survival of ER+ P-ILCs and TN-P-ILCs, respectively. For HER2+ P-ILCs, Ki-67 > 20% and sTILs ≤ 10% were significant factors for lower DFS. P-ILCs is an aggressive subtype of ILCs. Analyzing the prognostic factors of P-ILCs with heterogeneous morphological and biomarker characteristics is helpful for creating an individualized treatment.

Abstract P1-02-08: Comparison of clinical features and outcomes for pleomorphic invasive lobular carcinoma vs. non-pleomorphic invasive lobular carcinoma

Abstract Background: Invasive lobular carcinoma (ILC) is the second most common invasive breast cancer histology. Within ILC histology, there are multiple subtypes. The most common subtype is “classic” characterized by small single files of cells invading the stroma. Another subtype of clinical interest is “pleomorphic” which is characterized by larger cells with varied nuclear appearance. Rare and not well understood, pleomorphic ILC is traditionally viewed as an aggressive form of ILC. Studies have shown a relatively consistent association between pleomorphic ILC and certain high risk features such as advanced stage, HER2 positivity, and lymph node involvement. Survival outcome data comparing pleomorphic ILC to non-pleomorphic ILC has yielded varied results. Methods: A retrospective study of a large institutional database was conducted to characterize patients with ILC treated from 2004-2017. Patient and disease characteristics were recorded, including disease staging, biomarker profile, specific ILC histology, treatment details, and recurrence events. Findings were analyzed and overall survival (OS) and recurrence free survival (RFS) were compared between pleomorphic and non-pleomorphic ILC cohorts. Propensity score matching was also completed to account for confounding variables. Results: A total of 691 patients who had surgery were studied (mean age 61.6 ± 11.6 years old, 86.9% Caucasian, 98.3% with endocrine therapy), including 100 (14.4%) with pleomorphic ILC and 591 (85.5%) with non-pleomorphic ILC. Compared to non-pleomorphic ILC, pleomorphic ILC was less likely to be estrogen receptor (ER) positive (94% vs. 98%, p=0.004), more likely to be HER2 positive (12% vs. 7%, p=0.07), more likely to be grade 3 (33% vs. 2%, p&amp;lt;0.001), less likely to be diagnosed at a lower T stage (Stage I 38% vs. 58%, Stages II-III 61% vs. 41%, p&amp;lt;0.001), and less likely to be diagnosed with axillary lymph node involvement (node positivity 48.5% vs. 66%, p&amp;lt;0.001). Mastectomy rates were 65% in pleomorphic ILC and 52% in non-pleomorphic ILC (p=0.022). Patients with pleomorphic ILC were more likely to receive chemotherapy (66% vs. 36%, p&amp;lt;0.001). Pleomorphic ILC patients were also more likely to receive HER2-directed therapy (12% vs. 5.8%, p=0.02). Median follow-up was 6 years. There was no significant difference in OS and RFS between cohorts before matching for age, BMI, stage, surgery type, and chemotherapy. Although not statistically significant, pleomorphic ILC appears to have better RFS and OS between propensity score matched 91 pairs (10-year RFS: 79% vs. 71.5%, p=0.27 and 10-year OS: 86% vs. 76%, p=0.13). Exploratory analysis also suggests that multifocal pleomorphic ILC is associated with worse RFS and OS compared to unifocal pleomorphic ILC. Conclusions: Pleomorphic ILC was found to have more advanced disease at presentation in the breast but not in lymph nodes. At our institution, it was treated with more chemotherapy compared to non-pleomorphic ILC, likely related to higher grade, lower ER-positivity, and higher HER2-positivity. After propensity score matching, pleomorphic ILC appears to have better RFS and OS compared to non-pleomorphic ILC. This was particularly noticeable three years after surgery and may reflect more aggressive management. These data reveal some unexpected trends that challenge the notion of pleomorphic ILC having worse outcomes compared with non-pleomorphic ILC. This highlights the need for additional studies to better understand multiple aspects of ILC and its subtypes. Citation Format: Matthew D. Wright, Marcus S. Dempster, Ayat ElSherif, Daniela Cocco, Stephanie A. Valente, Hong Li, Megan L. Kruse. Comparison of clinical features and outcomes for pleomorphic invasive lobular carcinoma vs. non-pleomorphic invasive lobular carcinoma [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 P1-02-08.

Abstract P1-08-13: Comparison of gene expression profiling results and clinical outcomes among patients with pleomorphic ILC and classic ILC

Abstract Background Invasive lobular carcinoma (ILC) is the second most common histological subtype of breast cancer. Pleomorphic ILC (pILC) is a pathologically defined subtype of ILC that often presents at a higher stage compared to Classical ILC (cILC). pILC is traditionally thought to have poor outcomes compared with cILC. Utility and application of gene expression profiling, such as Oncotype Dx testing, for these patients is unknown. The purpose of this study is to compare Oncotype Dx recurrence scores, treatment patterns, and clinical outcomes for patients with cILC and pILC at our institution. Methods A retrospective analysis of a large institutional cancer database was performed to identify patients with ILC treated between 2004 and 2017. Patient and disease characteristics were collected, including subtype of ILC (classical vs pleomorphic), staging, treatment history, and presence of Oncotype Dx testing. Findings were analyzed for differences in clinical characteristics, Oncotype Dx results, progression free survival (PFS) and overall survival (OS) between patients who received endocrine therapy/chemotherapy (CET) versus endocrine therapy alone (ET) in both cILC and pILC groups. Results: 692 patients with ILC were identified with 100 (14.5%) categorized as pILC. The mean age at presentation was 62 for cILC and 60 for pILC. cILC was more frequently ER positive (98.5% vs. 94.0%, p=0.004). and less likely HER2 positive (7.0% vs 12.2%, p=0.07). pILC more commonly had more advanced tumor stage (Stages II-III 61% vs 41%, p&amp;lt;0.001) but lower nodal stage (N+ 48.5% vs 66%, p&amp;lt;0.001) 25% (25/100) of pILC patients had Oncotype Dx testing performed compared to 33% (198/592) of cILC patients. The majority of patients who had testing had T1cN0 or T2N0 disease (36% and 44% for pILC vs 34%, and 27% for cILC, respectively). A low risk recurrence score (0-10) accounted for 8% (2/25) of pILC cases and 18.2% (36/198) of cILC. Intermediate risk (11-25) accounted for 72% (18/25) of pILC and 73.2% (145/198) of cILC. High risk (26+) accounted for 20% (5/25) of pILC and 8.6% (17/198) of cILC. There was no statistically significant difference in Oncotype Dx recurrence score distribution between pILC and cILC (p=0.117). More patients with pILC received CET compared to cILC (62.0% vs 36.7%, p&amp;lt;0.001). Among pILC cases, 62% received CET and 34% received ET. There was no significant difference in RFS or OS between CET and ET among pILC cases (10-year RFS 74.7% (ET) vs. 76.6% (CET), p=0.52. 10-year OS 92.6% (ET) vs 78.0% (CET), p=0.40). Conclusions At our institution, patients with cILC more often had Oncotype Dx testing compared to those with pILC. Some of the difference may be related to more frequent HER2-positivity in pILC. When testing was done, pILC was twice as likely to have a high risk recurrence score compared to cILC, but this result was not statistically significant. Patients with pILC were more likely to receive CET than patients with cILC. There was no difference in survival between patients with pILC treated with CET versus those treated with ET alone although the sample size is small and this is worthy of further study in a larger population. These results suggest that gene expression testing may be underutilized in pILC. Citation Format: Marcus Dempster, Matthew Wright, Daniela Cocco, Ayat Elsherif, Stephanie A Valente, Hong Li, Megan L Kruse. Comparison of gene expression profiling results and clinical outcomes among patients with pleomorphic ILC and classic 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 P1-08-13.

Clinicopathological Features, Tumor Mutational Burden, and Tumour-Infiltrating Lymphocyte Interplay in ERBB2-Mutated Breast Cancer: In Silico Analysis.

Recent evidence suggests that somatic mutations in ERBB2 activate ERBB2 signaling. These mutations occur at a frequency of approximately 3% in breast cancer (BC). ERBB2 mutations indicate poor prognosis as they are associated with recurrence and metastasis. This study aimed to evaluate the clinicopathological features, immune infiltration levels, tumor mutational burden (TMB), and tumor-infiltrating lymphocytes (TILs) in ERBB2-mutated breast cancer (ERBB2-mutated BC) using a bioinformatic approach and publicly available datasets (i.e., TCGA-BRCA and TIMER2.0). ERBB2-mutated BCs were associated with a high histological grade. ERBB2-mutated BCs comprised invasive breast carcinoma of no special type (21/35, 60%), classic invasive lobular carcinoma (12/35, 34.3%), and pleomorphic invasive lobular carcinoma (2/35, 5.7%). A Kaplan-Meier survival curve demonstrated that ERBB2-mutated BC was associated with a significantly worse prognosis compared to ERBB2 non-mutated BC (p < 0.01). Furthermore, 40% (14/35) of the patients with ERBB2-mutated BC harbored CDH1 mutations. Mutations at L755 and V777 accounted for 30.5% of these mutations in ERBB2-mutated BC, suggesting that these sites are mutational hot spots in BC, particularly in invasive lobular carcinoma. Of the ERBB2-mutated BCs, 8.6% were classified as TIL-high, whereas 77.1% were TILs-low; TMB significantly correlated with TILs (p < 0.05). CD8+ T cell infiltration levels were significantly higher in ERBB2 non-mutated BC. Among ERBB2-mutated BCs, 22.9% were classified as TMB-high, which was significantly higher than the rate in the ERBB2 non-mutated BC (p < 0.01). These findings provide evidence for a link between ERBB2 mutations and high TMB in BC.

Clinicopathological characteristics and prognostic marker of triple-negative breast cancer in older women

Triple-negative breast cancer (TNBC) lacks an effective treatment target and is usually treated with chemotherapy. Treatment of older patients with TNBC, however, should be decided carefully because of the side effects of chemotherapy in this population. Some forms of TNBC are associated with a favorable prognosis and do not require chemotherapy. To optimize the treatment of older patients with TNBC, it is important to know the clinicopathological characteristics and a prognostic marker. In this study, classic clinicopathological factors, immunohistochemical characteristics (androgen receptor [AR], cytokeratin 5/6 [CK5/6], epidermal growth factor receptor), tumor-infiltrating lymphocytes (TILs), and the clinical outcome based on the status of each biomarker were compared among a consecutive series of female patients with TNBC aged ≥75 years (n = 75) and among those aged 55–64 years matched for the pathological stage (n = 47) who underwent surgery without neoadjuvant therapy. TNBC with special histology (particularly apocrine carcinoma, pleomorphic invasive lobular carcinoma, and metaplastic carcinoma) was more frequent in the older group than in the younger group (35/75, 57% versus 11/47, 23%, P = 0.010). The AR positivity rate was higher in older patients than in younger patients, whereas TILs and CK5/6 exhibited the opposite results. In multivariate analyses, AR positivity was an independent predictor of a favorable outcome in older patients (lower recurrence rate), whereas the high level of TILs was favorable in younger patients (lower recurrence and mortality rates). AR positivity or apocrine morphology was frequent and predicts a favorable clinical outcome in older patients with TNBC, suggesting the importance of AR examination in this population.

Clinicopathological and Molecular Characteristics of Pleomorphic Invasive Lobular Carcinoma.

Pleomorphic invasive lobular carcinoma (PILC) is a distinct morphological and biologically aggressive variant of invasive lobular carcinoma (ILC). We hypothesized that was due to de novo activation of PI3K/Akt/mTOR pathway in PILC resulting in higher proliferation rate and markers of cell cycle activation. We identified PILC and ILC tumors and tested for PI3K/Akt/mTOR pathway activation by immunohistochemistry (PTEN and pS6K1) and gene expression analysis (by Nanostring nCounter system). Proliferation index (Ki67) was elevated in 85% of PILCs compared to 20% of ILCs (p < 0.007). PTEN expression was high in all while pS6K1 was high in 8/9 PILCs compared to 3/9 ILCs (p < 0.007). Gene expression analysis shows that PILCs have overexpression of genes involved in cell cycle proliferation, cellular proliferation, DNA damage, and repair genes but no difference in PI3K/Akt/mTOR pathway genes. PILCs are a biologically distinct group of ILC, and clinicopathological characteristics suggest they would have a more clinically aggressive behavior. In addition, our results indicate that PI3k/Akt/mTOR pathway and cell cycle proliferation are activated in majority of these tumors. Further studies are needed to investigate these mechanisms as there are approved therapies available that may benefit PILCs.

Mitotic score and pleomorphic histology in invasive lobular carcinoma of the breast: impact on disease-free survival.

Pleomorphic invasive lobular carcinoma (ILC) has long been thought to have worse outcomes than classic ILC and is therefore often treated with chemotherapy. However, recent data question the utility of the pleomorphic designation, as the poor outcomes seen may be related to other associated high-risk features. Importantly, mitotic count may better define a subset of ILC with high risk of recurrence. We sought to determine the impact of pleomorphic histology versus mitotic count on disease-free survival (DFS) in pure ILC. Additionally, we evaluated whether pleomorphic histology was associated with receipt of chemotherapy when adjusting for other factors. We analyzed a cohort of 475 patients with stage I-III pure ILC. We used Kaplan-Meier estimates, and Cox proportional hazards and logistic regression for multivariate analyses. Pleomorphic histology was confirmed by central pathology review. In a multivariate model, pleomorphic histology was not associated with reduced DFS. Only mitotic score, receptor subtype, and pathologic stage were independently and significantly associated with DFS. Patients with pleomorphic ILC were significantly more likely to receive chemotherapy than patients with classic ILC (adjusted odds ratio 2.96, p = 0.026). The pleomorphic designation in ILC does not have clinical utility and should not be used to determine therapy. Rather, mitotic count identified clear prognostic groups in this cohort of pure ILC.

Abstract P5-02-09: The prevalence of invasive lobular carcinomas with unconventional immunohistochemical phenotypes

Abstract Background The prognosis of invasive lobular carcinoma (ILC) is controversial. Some studies report equivalent or better outcomes than invasive ductal carcinoma, likely due to ILC’s favorable prognostic phenotype. Classic ILC (CL) is typically of low histologic grade, estrogen receptor (ER) positive and human epidermal growth factor receptor-2 (HER2) negative. However, worse long term outcomes have been observed because ILC tends to be multicentric, bilateral, and to show higher rates of late metastases in uncommon sites. Additionally, subtypes of ILC, including solid (SOL) and pleomorphic (PL), have been reported to display more aggressive behavior. Yet current treatment paradigms are distinguished by hormone receptor profile and stage, not by tumor morphology. This study aimed to evaluate the clinicopathologic and immunohistochemical (IHC) characteristics of ILC, particularly those with unusual patterns. Methods From 2009-2018, consecutive in-house biopsy and resection specimens with the diagnosis of ILC were identified by a retrospective review of our institutional database. Demographic, morphologic, and IHC data were obtained from pathology reports. Cases with equivocal HER2 IHC results are sent for fluorescence in situ hybridization analysis at our Center. CL ILC was defined by small cells with low nuclear grade and discohesive growth arranged in single file or cords. PL ILC is composed of larger, more atypical cells, which still exhibit discohesion typical of lobular phenotype. SOL ILC consists of tumors growing in large sheets with minimal intervening stroma. Results Over the nine year study period, a total of 3,028 ILCs from 2,322 patients were identified. Most (74%, 2229/3028) cases were classified as CL while 22% (665/3028) were PL and 4% (134/3028) SOL (Table 1). The median patient age was 60 years (range 32-95). The median tumor size was larger for PL (2.3 cm) and SOL (2.4 cm) subtypes than CL (1.1 cm). IHC results were available for 896 specimens. The majority of all ILCs showed an expected phenotype: ER positive and HER2 negative (99% CL, 84% PL, 97% SOL). A smaller subset of ER positive ILC were also HER2 positive (1% CL, 8% PL, 3% SOL). No CL or SOL ILC were ER negative; in contrast 8% (21/270) of PL ILC were ER negative. Twelve (5%) PL ER negative cases were also HER2 negative. Overall, 15% of ILC were HER2 positive, with the PL variant showing the highest incidence (11%, 30/270). Lymph node (LN) metastases were seen in 22% (66/291) of CL cases, 55% (53/96) PL and 29% (17/58) SOL. Metastases in 10 or more LN (N3) was seen only in PL and SOL cases (13% and 5%, respectively). Conclusions In this study, up to 8% of ILC cases were found to be ER negative, a finding unique to the PL variant. No CL or SOL ILC was ER negative. HER2 positivity, not typically expected in ILC, was seen in 15% of cases, most commonly in the PL type. ILC that was both negative for ER and HER2 was observed in 5% of cases, and only within the PL subgroup. PL ILC showed higher median tumor size at presentation than CL and nodal metastases were also more common in PL than in CL or SOL ILC (55% vs 22% and 29%, respectively). Our findings are in keeping with prior observations that compared to CL ILC. PL ILC exhibits features associated with unfavorable clinicopathologic features, such as higher tumor and nodal stage at presentation. Additionally, this is the first study to systematically examine the prevalence of unconventional IHC phenotypes of ILC (ER negativity and/or HER2 positivity) in a large series from one institution. Table 1. Summary of Clinicopathologic FeaturesClassicPleomorphicSolidILC types (n=3028)2229665134Median age, (range)60 yrs (32-94)61 yrs (31-95)66 yrs (44-93)Median size, cm 1.12.32.4Immunophenotype (n=896)ER+/HER2-99% (551/559)84% (228/270)97% (65/67)ER+/HER2+1% (8/559)8% (21/270)3% (2/67)ER-/HER2+0% (0/559)3% (9/270)0% (0/67)ER-/HER2-0% (0/559)5% (12/270)0% (0/67)Lymph node status (n=445)N077% (225/291)45% (43/96)71% (41/58)N120% (59/291)31% (30/96)19% (11/58)N22% (7/291)11% (11/96)5% (3/58)N30% (0/291)13% (12/96)5% (3/58) Citation Format: Matthew G Hanna, Anne Grabenstetter, Dara S Ross, Lee K Tan. The prevalence of invasive lobular carcinomas with unconventional immunohistochemical phenotypes [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-02-09.

Pleomorphic Invasive Lobular Carcinoma of the Breast With Extracellular Mucin and HER2 Amplification

Pleomorphic Invasive Lobular Carcinoma of the Breast With Extracellular Mucin and HER2 Amplification

A comparison of the imaging features of pleomorphic and classical invasive lobular carcinoma.

Pleomorphic invasive lobular carcinoma (pILC) is a distinct morphological variant of ILC with a poorer prognosis than classical ILC (cILC). The aim of this study was to ascertain whether the conventional imaging appearances of the two entities differ. A single-center retrospective review of conventional imaging was undertaken in 150 consecutive patients with histopathologically confirmed ILC (38 pILC; 112 cILC) between April 2010 and July 2015. Mammographic and sonographic findings were evaluated using the BI-RADS lexicon by a radiologist blinded to pathology, and the findings in the two groups were compared. The degree of discrepancy between imaging and pathological sizing in the two groups was evaluated. Lesions were mammographically occult in 11% of pILC and 14% of cILC (p = 0.56). On mammography, skin or trabecular thickening and microcalcification were commoner in pILC than cILC (13% vs. 1%, p < 0.01; 25% vs. 5%, p < 0.01). Architectural distortion was more frequent in cILC than pILC (26% vs. 9%, p = 0.01). On ultrasound, pILC more frequently exhibited mixed echogenicity (28% vs. 13%; p = 0.04), skin thickening, subcutaneous or parenchymal edema (8% vs. 0%; p = 0.02), echogenic surrounding fat (33% vs. 9%; p < 0.01), and posterior acoustic enhancement (10% vs. 1%; p = 0.02) than cILC. CILC was more frequently manifested as a focal area of altered echogenicity (24% vs. 8%; p = 0.04). Mean elastography stiffness was higher for pILC (174.8 vs. 124.6kPa; p = 0.02). Imaging-pathological size disparity was similar for both subtypes. There are differences in the imaging features between pILC and cILC which reflect the more aggressive nature of pILC.

Pleomorphic lobular carcinoma: is it more similar to a classic lobular cancer or to a high-grade ductal cancer?

BackgroundPleomorphic invasive lobular carcinoma (P-ILC) is an uncommon variety of invasive lobular carcinoma with aggressive clinical features. Little is described in the literature regarding this topic.Materials and methodsWe reviewed our experiences from 2010 to 2015 and compared 40 patients with P-ILC, 126 patients with classic-ILC (C-ILC) and 574 cases of high-grade invasive ductal carcinoma (HG-IDC). We studied the histologic and immunohistochemical features, clinical presentation and surgical treatment.ResultsP-ILC is diagnosed at the same age and tumor diameter as those of the other two histologic types. It is associated more frequently with multiple lymph node metastases and high proliferative index, and HER2/neu is amplified in 10% of cases. In spite of sharing some histologic characteristics with C-ILC (same growth pattern, loss of E-cadherin expression, same genetic pathway), its clinical and pathologic features define an autonomous entity. Its surgical treatment is similar to those of C-ILC and HG-IDC.ConclusionThis is the first review comparing these three pathologic entities. Our findings may be useful in understanding this variety of invasive lobular carcinoma, and further studies are certainly needed in this field.

P044 - Clinicopathologic features of pleomorphic invasive lobular carcinoma: comparison with classic invasive lobular carcinoma

P044 - Clinicopathologic features of pleomorphic invasive lobular carcinoma: comparison with classic invasive lobular carcinoma