Invasive Lobular Carcinoma Patients Research Articles

Oncologic Safety of Immediate Oncoplastic Surgery Compared with Standard Breast-Conserving Surgery for Patients with Invasive Lobular Carcinoma.

Invasive lobular carcinoma (ILC) of the breast grows in a diffuse pattern, resulting in a high risk of positive margins at surgical resection. Oncoplastic approaches have been shown to reduce this risk, but concerns persist around the safety of immediate oncoplastic surgery for those with ILC. This study evaluated the short- and long-term oncologic outcomes of immediate oncoplastic surgery for patients with ILC. This study retrospectively analyzed an institutional database of stages I to III ILC patients who underwent breast-conserving surgery (BCS) with or without immediate oncoplastic surgery (oncoplastic closure or oncoplastic reduction mammoplasty [ORM]). The study compared positive margin rates, rates of successful BCS, and recurrence-free survival (RFS) by type of surgery. For 494 patients the findings showed that the use of immediate ORM was associated with significantly lower odds of positive margins (odds ratio [OR], 0.34; 95 % confidence interval [CI], 0.17-0.66; p = 0.002). Both lumpectomy with oncoplastic closure and ORM were significantly associated with higher rates of successful BCS than standard lumpectomy (94.2 %, 87.8 %, and 73.9 %, respectively; p < 0.001). No difference in RFS was observed between those undergoing immediate oncoplastic surgery and those undergoing standard lumpectomy alone. The patients with stages I to III ILC who underwent immediate oncoplastic surgery had significant benefits including lower odds of positive margins and higher rates of successful BCS, with both types of immediate oncoplastic surgery showing similar RFS compared with lumpectomy alone. This supports the oncologic safety of immediate oncoplastic surgery for diffusely growing tumors such as ILC, providing it an ideal option for patients desiring BCS.

Abstract PO1-15-03: Spatially resolved analysis of tumor microenvironment in invasive lobular carcinoma

Abstract Background: Invasive lobular carcinoma (ILC) is the second most common histological breast cancer subtype; however, little is known about its tumor microenvironment (TME). Here, we aimed to study ILC TME using spatial transcriptomics (ST). Methods: We performed ST (Visium 10x Genomics) on frozen tumor samples from 43 primary hormone receptor positive (HR+), HER2-negative (HER2-) ILCs. Of note, 9 samples were coming from patients who experienced disease relapse. Relative hematoxylin/eosin (H&amp;E) slides were morphologically annotated (QuPath software). xCell was used to perform cell type enrichment analysis on sample pseudo-bulks. After cross-samples integration, ST spots were clustered using hierarchical clustering (STutility R package). intNMF algorithm was used to perform clustering at the patient-level by combining: RNA sequencing information (relative percentage of spot-level clusters in each sample), morphology and level of colocalization between cancer cells and the other cell types of the tumor microenvironment. METABRIC (HR+, HER2- ILC samples, n = 122) was used as external validation cohort. Survival analyses (univariable and multivariable adjusting for clinicopathological features) were performed using Cox proportional hazard models. Results: The patient-level classification revealed four groups showing different biological characteristics. Differences in terms of morphology (annotation) and pathway enrichment analysis based on marker genes (GSEA) were observed between groups. This information allowed us to annotate our groups as: proliferative (P, n = 12, enriched in tumor cells and proliferation-related pathways), normal-stroma enriched (NSE, n = 10, enriched in fibroblasts and carcinoma in situ), metabolic (M, n = 9, enriched in metabolic-related pathways) and metabolic-immune enriched (MIE, n = 10, enriched in adipose tissue, metabolic and immune-related pathways). Interestingly, a significantly higher presence of macrophages M2 was found in MIE group. Using group-specific gene signatures, we were able to reproduce the same 4 groups in the METABRIC. Of note, we observed significant differences in relapse-free survival (RFS) in METABRIC (p = 0.03), with NSE presenting better outcome, while P, M and MIE presented worse prognosis. Analysing the area of contact between adipocytes and cancer cells typical of MIE group, we noticed an enrichment in metabolic and M2 macrophages-related pathways. In doing so, we derived a 28 gene signature relative to the tumor-adipocytes contact area. Importantly, our signature was highly expressed in M and MIE groups, and it was not correlated with proliferation-related signatures. Interestingly, the adipocytes-related signature was significantly associated with shorter RFS in ILC patients in METABRIC (univariable: HR 1.4, p = 0.023; multivariable: HR 1.6, p = 0.005). Since both proliferation and metabolism showed to be key processes in defining prognosis in ILC, we built a prognostic index by integrating our adipocytes-related signature with genomic grade index (GGI, a proliferation-related signature). Our index outperformed other existing prognostic signatures (e.g., Oncotype DX, MammaPrint, EndoPredict, LobSig) in assessing prognosis (RFS) in ILC in METABRIC (univariable: HR 1.7, p &amp;lt; 0.001; multivariable: HR 1.7, p = 0.002). Conclusions: We identified 4 biologically driven HR+, HER2- ILC groups describing tumor microenvironment heterogeneity. Of note, two of the three groups associated to worse disease outcome were related to metabolism, highlighting the importance of such process in ILC biology and in the future development of new treatment strategies. Moreover, the prognostic power of our index has the potential to refine the assessment of the risk of relapse in ILC. Further validation is warranted. Citation Format: Matteo Serra, Mattia Rediti, Laetitia Collet, Frédéric Lifrange, David Venet, Nicola Occelli, Xiaoxiao Wang, Delphine Vincent, Ghizlane Rouas, Ligia Craciun, Denis Larsimont, Laurence Buisseret, Miikka Vikkula, François Duhoux, Françoise Rothé, Christos Sotiriou. Spatially resolved analysis of tumor microenvironment in 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 PO1-15-03.

Abstract PO4-02-12: MDA iLobular Prognostic Tool: A Novel Approach for Risk Stratification in Invasive Lobular Carcinoma

Abstract Background: Invasive lobular carcinoma (ILC) is a distinct subtype of breast cancer that differs from the more common invasive ductal carcinoma (IDC) by its unique characteristics that influence prognosis. Recent studies have shown that ILC is associated with worse long-term outcomes compared to IDC. Risk stratification is essential in breast cancer for tailoring treatment plans to the individual patient’s needs, maximizing the chances of successful outcomes and minimizing unnecessary interventions. Although there are multiple tools available for breast cancer, there is currently not a risk stratification tool that is specific for ILC. The MDA iLobular prognostic tool is the first risk stratification tool that has been developed specifically for ILC patients. Methods: We retrospectively searched for patients treated at MD Anderson Cancer Center with a diagnosis of stage I-III ILC in our prospectively collected electronic database. The study focused on two primary endpoints: Overall Survival (OS) and Distant Recurrence Free Survival (DRFS). We utilized univariate and multivariate Cox Proportional Hazard (PH) regression models to assess the statistical significance of all variables. The univariate Cox analysis identified prognostic factors, which were further analyzed using backward and stepwise multivariate Cox proportional hazards regression analysis. This process helped identify statistically significant prognostic factors that were included in the final multivariate models. We estimated hazard ratios and 95% confidence intervals for each factor, considering a P-value of &amp;lt; 0.05 as statistically significant. To evaluate the performance of the fitted multivariate Cox PH regression models for OS and DRFS, we randomly divided two-thirds of the data points into a training dataset, while the remaining one-third constituted the test dataset. We assessed the discrimination capacity of each model using Harrell's C-index. Results: The study included a total of 4,216 female patients, with a median age of 56 years. The median pathological tumor size was 2 mm, and the median number of lymph nodes was one. Among these patients, 1,376 were pre-menopausal, while 2,837 were post-menopausal. The training cohort was a subset of 2,950 patients and the test cohort was a subset of 1,266 patients. After evaluating various prognostic models, we identified the model with the highest prognostic accuracy for OS and DRFS. This selected model demonstrated a Harrell's C-index of 0.704 for OS and 0.718 for DRFS on the training dataset and a Harrell's C-index of 0.702 for OS and 0.671 for DRFS on the test dataset. The model incorporated several covariates, including age at the time of diagnosis, number of lymph nodes, pathological tumor size (mm), ER status, tumor grade, ILC histology, and the presence or absence of concomitant LCIS (Table 1). Conclusion: In conclusion, the MDA iLobular prognostic tool represents a significant advancement as the first dedicated tool for risk stratifying ILC, providing valuable guidance for tailoring therapy to individual ILC patients based on their specific risk profiles. Table 1. Multivariate Cox proportional hazard model parameter estimates for OS and DRFS Citation Format: Jason Mouabbi, Sarah Pasyar, Roland Bassett, Akshara Singareeka Raghavendra, Amy Hassan, Rachel Layman, Debu Tripathy. MDA iLobular Prognostic Tool: A Novel Approach for Risk Stratification in 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 PO4-02-12.

Abstract PO4-02-03: Distribution of MammaPrint, BluePrint, and Response Predictive Subtypes based on ImPrint and Reprint in ER+/HER2- Invasive Lobular Carcinoma – A FLEX sub study

Abstract Background: Invasive lobular carcinoma (ILC), the second most common histologic subtype of breast cancer, is increasingly recognized as a distinct tumor type compared to the more common invasive ductal carcinoma (IDC). While ILC is known to have lower rates of pathologic complete response to neoadjuvant chemotherapy, ILC tumors are biologically heterogenous. As such, genomic signatures might identify patients with ILC who might benefit from tailored treatment options. The gene expression signature MammaPrint (MP) classifies tumors as having a Low Risk or High Risk of distant recurrence. MP combined with BluePrint (BP), a molecular subtyping signature, categorizes tumors as Luminal A (MP Low Risk), Luminal B (MP High Risk), Basal or HER-2 type. ImPrint is a 53-gene signature that identifies HR+HER2- patients predicted to benefit from immune checkpoint inhibitors. RePrint is a 60-gene DNA repair deficiency (DRD) signature that identifies HR+HER2- patients who may benefit from PARP inhibitors with platinum agents. Response Predictive Subtypes (RPS), used in the I-SPY2 trial, combine clinical subtype and these genomic signatures to personalize treatment planning and improve outcomes. In this study, we determined the distribution of 3 RPS in HR+HER2-: (1) ImPrint-/RePrint-, (2) ImPrint-/RePrint+ (3) ImPrint+, in patients ILC compared to IDC enrolled in the FLEX trial. Methods: This study includes 1078 HR+HER2-women with ILC and 6078 with IDC enrolled in FLEX registry. FLEX (NCT03053193) is a prospective, observational trial that includes stage I-III breast cancer patients who undergo MammaPrint testing (with or without BluePrint) as standard of care, and consent to full transcriptome and clinical data collection. MP High Risk tumors were further stratified into High 1 and High 2. ImPrint and Reprint results were used to determine RPS. A two-tailed proportional z-test was used to assess differences between ILC and IDC as well as between RPS. Results: ILC patients had a significantly lower percentage of MP High Risk tumors in comparison to IDC. Among MP High Risk tumors, those with ILC had significantly more MP High 1 than patients with IDC. BP subtyping in ILC tumors showed significantly lower percentage of Basal, and Luminal B, and higher percentage of Luminal A compared to IDC tumors. For RPS, a higher percentage of ILC tumors were ImPrint-/RePrint- compared to IDC, whereas lower frequencies of ImPrint-/RePrint+ and ImPrint+ were found. Within the ILC ImPrint+ subgroup (n=14), 1 (7.1%) was classified as High 2 and 10 (71.4%) as High 1 and 3 (21.4%) as Low Risk. All 14 (100%) ImPrint+ patients were BP Luminal. In contrast, within the IDC MP High Risk ImPrint+ subgroup (n=328), 233 (71.0%) were High 2, 88 (26.8%) High 1 and 7 Low Risk (2.1%). Furthermore 193 (60.7%) were classified as BP Basal, 2 HER2 (0.6%) and 123 (38.7%) Luminal within this IDC RPS. Conclusions: This is the first study to investigate the distribution of Response Predictive Subtypes in ILC, which will be beneficial to optimize the treatment selection for patients with early-stage HR+/HER2- ILC. Though the percentage of ImPrint+ is lower in ILC, this study revealed a small subset of patients in ILC with potential response to Immunotherapy. Furthermore, these results underscore the heterogeneity of ILC tumors and generate further hypotheses to investigate the immune cell abundance in ILC compared to IDC and correlate immune cell abundance to ImPrint status. Table: Genomic and Tumor Characteristics of HR+HER2- ILC and IDC tumors Citation Format: Rita Mukhtar, Christina Yau, Denise Wolf, Adam Brufsky, Hannah Linden, Natasha Hunter, Reshma Mahtani, Abirami Sivapiragasam, Trevor Feinstein, Fengting Yan, Ian Grady, Priscilla McAuliffe, Michaela Tsai, Joyce O'Shaughnessy, Blanche Mavromatis, Sasha Davis, Josien Haan, William Audeh, Lavanya Samraj, FLEX Investigators' Group. Distribution of MammaPrint, BluePrint, and Response Predictive Subtypes based on ImPrint and Reprint in ER+/HER2- Invasive Lobular Carcinoma – A FLEX sub study [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 PO4-02-03.

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 PO4-17-03: Neoadjuvant chemotherapy in invasive lobular carcinoma of the breast: A retrospective study on survival outcomes

Abstract Background: Neoadjuvant chemotherapy (NAC) is a well-established component of breast cancer management. Invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC) are often treated similarly, but many studies are demonstrating a major difference in treatment responses according to the histopathological type of cancer. Aim: To evaluate the overall survival of patients with ILC after NAC compared with adjuvant chemotherapy. Methods: This retrospective cohort study included patients treated for breast ILC between 1998 and 2016 at the Center for Breast Diseases of de CHU de Québec – Université Laval, a tertiary breast cancer center. The primary outcomes were the overall survival (OS) and the recurrence-free survival (RFS) of ILC patients receiving NAC compared with patients who received only adjuvant chemotherapy. The follow-up was censored at the last hospital contact. The secondary outcomes were the locoregional recurrence, pathological complete response (pCR), and pCR impact on survival. Results: During the study period, 265 women were treated for ILC, of which 72 had NAC, and 193 had adjuvant therapy. No significant differences were observed regarding the patient’s characteristics (age, BMI, smoking, menopausal status, and use of hormonal replacement therapy). A T4 disease was found in 29.2% of the NAC group (vs. 0 in the adjuvant group), but the N2-3 rate was lower in the NAC group (5.6% vs. 22.3%, P=0.011). More patients in the NAC group underwent mastectomy (65.3% vs. 29.5%, P&amp;lt; 0.0001) and axillary dissection (80.6% vs. 50.8%, P&amp;lt; 0.0001). Three (4.2%) patients in the NAC group achieved a pCR. The rates of radiotherapy (P=0.851) and hormonal therapy (P=0.694) were similar between the two groups. The mean follow-up was 8 years. After adjustment for age, T, N, surgery type, radiotherapy, and hormonal therapy, the NAC group showed significantly lower 10-year OS (56.2% vs. 80.7%, P&amp;lt; 0.0001) and RFS (51.8% vs. 72.7%, P=0.0004) compared with the adjuvant group. There were no differences in the 10-year local recurrence rate (90.6% vs. 93.5%, P=0.11). In a Cox regression analysis of RFS considering the previously mentioned covariables, more events in the NAC group (OR=2.52, 95%CI: 1.39-4.58, P=0.002) and patients with N2-N3 (OR=3.68, 95%IC: 2.00-6.80, P&amp;lt; 0.01). Conclusion: Despite the general belief that ILC and IDC should be treated similarly, this study strongly suggests that ILC seems to have a poorer response to NAC. Patients diagnosed with ILC might benefit from a more aggressive surgical approach followed by adjuvant chemotherapy, no matter the severity of the disease. Additional long-term prospective comparative studies are needed to support this statement and improve the management of these patients. Citation Format: Virginie Gauthier, Anne-Julie Simard, Christine Desbiens, Brigitte Poirier, Julie Lemieux, Dominique Boudreau, Dominique Leblanc, Claudya Morin, Jean-Charles Hogue, Éric Poirier. Neoadjuvant chemotherapy in invasive lobular carcinoma of the breast: A retrospective study on survival outcomes [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 PO4-17-03.

Abstract PO3-18-08: Rational therapeutic combination of Bromodomain and Extra-Terminal domain (BET) inhibitor and Fibroblast Growth Factor Receptor (FGFR) inhibitor for treatment of invasive lobular carcinoma

Abstract Background: Invasive lobular carcinoma (ILC) is the second most pervasive subtype after invasive ductal carcinoma (IDC), accounting for approximately 10-15% of all breast cancers. It is characterized by loss of E-cadherin expression and non-adherent tumor cells that invade the stroma in a “single-file” pattern. Women with ILC are typically diagnosed at an older age and later stage with ER-positive disease. ILC is more likely to exhibit late recurrence and metastasize to the gastrointestinal tract and urogenital tract compared with IDC. It is routinely treated with anti-endocrine therapy and chemotherapy, however, while not entirely chemo-refractory, displays a poor response to chemotherapy compared with IDC. As such, options for recurrent disease are limited and there is an urgent need to develop tailored therapy for ILC, especially for those patients that recur. The family of bromodomain and extra-terminal domain (BET) proteins, comprising BRD2/3/4/T, are epigenetic readers that bind to acetylated lysine residues on histones and recruit transcription factors to drive the expression of oncogenes. Previously. we discovered that BRD3 is a marker of poor prognosis in ILC and there is emerging evidence that BET inhibitors (iBET) are effective in diverse types of breast cancer. Here, we investigated the therapeutic potential of iBET in ILC, alone and in combination with FGFR inhibitors. Methods: IC50s for a panel of iBET using two typical ILC cell lines MDA-MB-134VI (MM134) and SUM44PE (SUM44) were determined. RNA-sequencing and Genexplain analysis was applied to reveal transcriptional networks, master regulators and potential resistance mechanisms. BRD3 and FGFR3 were knocked down using siRNA to evaluate their function in ILC cell lines. Furthermore, we utilized ILC cell-derived xenograft (CDX) models in SCID-beige mice established by mammary intraductal (MIND) implantation to evaluate the therapeutic potency of iBET alone or in combination with fibroblast growth factor receptor (FGFR) inhibitor in vivo. Results: We demonstrated that iBET significantly inhibited ILC cell growth in both 2D and 3D culture, with the greatest potency demonstrated by JQ1 and Mivebresib (ABBV-075). RNA-sequencing revealed dysregulated pathways in cell cycle division, DNA damage, apoptosis and MAPK signaling following iBET treatment. Reverse engineering of transcriptional profiles using Genexplain revealed that FGFR3 is a significantly upregulated master regulator (MTR) among 142 MTRs across both cell lines and both iBETs. Upregulation of FGFR3 after iBET treatment was verified at the protein level by Western blotting. We also show that BRD3 and FGFR3 knockdown significantly inhibited cell growth, which supports the key role both play in ILC progression. Further, we analyzed the iBET therapeutic effect when combined with the FGFR inhibitor, erdafitinib, as a strategy to overcome potential resistance due to FGFR upregulation post iBET treatment. This revealed that the combination of iBET and erdafitinib could inhibit ILC cell growth more effectively compared to using either agent alone. Furthermore, our in vivo study showed that JQ1 could inhibit tumor growth in a SUM44-MIND model and alleviate metastasis to peritoneum, bone and ovary compared with the vehicle group. Moreover, we also assessed the combination of mivebresib and erdafitinib in vivo. This revealed that iBET and an FGFR inhibitor work synergistically to decrease tumour burden and metastatic potential in both MM134-MIND and SUM44-MIND models. Conclusion: Our results provide evidence that iBET, either alone or in combination with erdafitinib, is remarkably effective at inhibiting ILC growth, both in vitro and in vivo and represents a rational therapeutic strategy for recurrent ILC patients in the future. Citation Format: Binbin Gao, Elspeth Ward, Anna Blümel, Emer Conroy, Rachel Moore, Grainne Cremin, Rachel Bleach, Kathryn Haley, Tríona Ní Chonghaíle, Andreas Lindner, Jochen Prehn, Yi Zhang, Idalia Cruz, Leena Hilakivi-Clarke, Georgios Sflomos, Cathrin Brisken, William Gallagher, Darran O'Connor. Rational therapeutic combination of Bromodomain and Extra-Terminal domain (BET) inhibitor and Fibroblast Growth Factor Receptor (FGFR) inhibitor for treatment of 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 PO3-18-08.

Comparison of long-term outcome between clinically high risk lobular versus ductal breast cancer: a propensity score matched study

Abemaciclib is currently approved for the adjuvant treatment of high-risk, lymph node (LN)-positive, hormone receptor (HR)-positive breast cancer (BC). In a real-world setting the clinicopathologic features of patients potentially eligible for adjuvant abemaciclib remain to be defined. There are conflicting data regarding the biological behavior and long-term outcomes across invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC). In our study we retrospectively assessed the real-world data and long-term outcome of selected high-risk features ILC compared to IDC, according to the MonarchE trial inclusion criteria. We identified 15,071 patients who got surgery at the European Institute of Oncology for a first primary, non-metastatic, HR-positive, HER2-negative BC from 2000 to 2008. 11,981 (79.5%) patients had an IDC and 1524 (10.1%) an ILC. The remaining 1566 patients (10.4%) had either combined ductal and lobular breast cancer or another histological breast cancer subtype. According to the eligibility criteria of the MonarchE study, we identified two high-risk groups, based on high number of positive lymph nodes, large tumor size, or a high cellular proliferation as measured by tumor grade or biomarkers. Patients were matched by propensity score. A total of 2872 (21.3%) patients were selected as clinically high-risk, including 361/1524 ILC (23.7%) and 2511/11,981 IDC (21%). 322 high-risk ILC were matched with similar high-risk IDC. The median follow-up was 13.2 years for survival. In the matched set, invasive disease-free survival (IDFS) (log-rank P=0.09) and overall survival (OS) (log-rank P=0.48) were not statistically significantly different between the two histological groups. For IDC patients, the 5-year and 10-year IDFS rates (95% CI) were 77.7% (72.9-82.2) and 57.3% (51.7-63.1) respectively, compared to the 5-year and 10-year IDFS rates of ILC patients that were 75.5% (70.6-80.2) and 50.7% (45.0-56.6). The 5-year and 10-year distant relapse free survival (DRFS) rates were 80% (75.3-84.2) and65.3% (59.8-70.7) in IDC cohort, compared to the 5-year and the 10-year DRFS rates of 78.7% (74.0-83.1) and 61.5% (55.9-67.1) in the ILC cohort. Such data match the recent outcomes efficacy results of the MonarchE control arm. More patients in the ILC (n=17) than in the IDC group (n=10) developed axillary recurrence. At multivariable analysis, stratified for specific clinical features, age <35 years, pT2-3, axillary involvement with more than 10 positive axillary nodes were found to be predictors of unfavorable IDFS and OS in the overall matched high-risk population. Findings from this matched cohort study reported similar IDFS and DRFS rates for high risk HR positive early BC when compared to the control arm overall IDFS and DRFS rates reported from the MonarchE trial. Our study demonstrated rates of concordant long-term outcome status beyond histologic subtype. These data support an escalation strategy for these two different histological entities when diagnosed with high-risk features. In our dataset approximately 21% rate of high-risk HR positive early BC patients are potentially eligible for adjuvant abemaciclib treatment. Umberto VeronesiFoundation.

Can 18F-FES PET Improve the Evaluation of 18F-FDG PET in Patients With Metastatic Invasive Lobular Carcinoma?

Invasive lobular carcinoma (ILC) exhibits a low affinity for 18F-FDG. The estrogen receptor (ER) is commonly expressed in ILCs, suggesting a potential benefit of targeting with the ER probe 18F-FES in this patient population. The objective of this study was to evaluate the diagnostic performance of 18F-FES imaging in patients with metastatic ILC and compare it with that of 18F-FDG. We conducted a retrospective analysis of 20 ILC patients who underwent concurrent 18F-FES and 18F-FDG PET/CT examinations in our center. 18F-FES and 18F-FDG imaging were analyzed to determine the total count of tracer-avid lesions in nonbone sites and their corresponding organ systems, assess the extent of anatomical regions involved in bone metastases, and measure the SUVmax values for both tracers. Among 20 ILC patients, 65 nonbone lesions were found to be distributed in 13 patients, and 16 patients were diagnosed with bone metastasis, which was distributed in 54 skeletal anatomical regions. The detection rate of 18F-FDG in nonbone lesions was higher than that of 18F-FES (57 vs 37, P < 0.001). 18F-FES demonstrated a superior ability to detect nonbone lesions in 4 patients, whereas 18F-FDG was superior in 5 patients (P > 0.05). Among 9/16 patients with bone metastasis, 18F-FES demonstrated a significant advantage in the detection of bone lesions compared with 18F-FDG (P = 0.05). Furthermore, patients with only 18F-FES-positive lesions (12/12) were administered endocrine regimens, whereas patients lacking 18F-FES uptake (2/3) predominantly received chemotherapy. 18F-FES is more effective than 18F-FDG in detecting bone metastasis in ILC, but it does not demonstrate a significant advantage in nonbone lesions. Additionally, the results of examination with 18F-FES have the potential to guide patient treatment plans.

68Ga-FAPI PET/CT as an Alternative to 18F-FDG PET/CT in the Imaging of Invasive Lobular Breast Carcinoma.

Accurate staging of invasive lobular carcinoma (ILC), a subtype of breast cancer, is vital for effective clinical management. Although 18F-FDG PET/CT is a commonly used tool, its efficacy varies across different histologic subtypes. To mitigate this challenge, our investigation delves into the potential utility of 68Ga-fibroblast activation protein inhibitor (FAPI) PET/CT as an alternative for staging ILC, aiming to address a significant research gap using a more expansive patient cohort than the smaller samples commonly found in the existing literature. Methods: In this retrospective analysis, women diagnosed with primary ILC of the breast underwent both 18F-FDG PET/CT and 68Ga-FAPI PET/CT. Both modalities were compared across all lesion locations with the used reference standard. The interval between scans was 1 wk, without any intervening treatments. Lesions were categorized visually, and tracer activity was analyzed using SUVmax, tumor-to-background uptake ratio, and uptake ratios. Both modalities were compared across various parameters, and statistical analysis was performed using SPSS 22.0. A P value of less than 0.05 was chosen to determine statistical significance. Results: The study included 23 female ILC patients (mean age, 51 y) with hormone-positive, human epidermal growth factor receptor type 2-negative tumors. Most (65%) had the luminal A subtype. 68Ga-FAPI PET/CT outperformed 18F-FDG PET/CT, with higher tumoral activity and tumor-to-background uptake ratios (P < 0.001). Primary tumors showed significantly increased uptake with 68Ga-FAPI PET/CT (P < 0.001), detecting additional foci, including multicentric cancer. Axillary lymph node metastases were more frequent and had higher uptake values with 68Ga-FAPI PET/CT (P = 0.012). Moreover, 68Ga-FAPI PET/CT identified more lesions, including bone and liver metastases. Pathologic features did not significantly correlate with imaging modalities, but a positive correlation was observed between peritumoral lymphocyte ratio and 68Ga-FAPI PET/CT-to-18F-FDG PET/CT uptake ratios (P = 0.026). Conclusion: This study underscores 68Ga-FAPI PET/CT's superiority over 18F-FDG PET/CT for ILC. 68Ga-FAPI PET/CT excels in detecting primary breast masses, axillary lymph nodes, and distant metastases; can complement 18F-FDG PET/CT in ILC; and holds potential as an alternative imaging method in future studies.

Abstract A052: Dissecting the immune regulatory mechanisms of distinct PI3K alterations in invasive lobular carcinoma

Abstract Immunotherapy has been far less effective in breast cancer compared to other cancer types, with only a small fraction of patients having clinical benefit. Historically, invasive lobular carcinomas (ILC), the second most common histological subtype of breast cancer, have been categorized as immunological cold tumors, but recent studies suggest that ILCs may recruit a myeloid-rich immunosuppressive immune landscape. Cancer cell intrinsic features such as the genetic makeup of tumor cells can dictate the spatial distribution, composition and activation state of immune cells, which can exert both anti-tumor and pro-tumor activities and affect disease progression and immunotherapy response. Genetic aberration in key genes of the phosphoinositide-3 kinase (PI3K) signaling pathway are observed in &amp;gt;50% of primary ILCs. The overall aim of this project is to determine whether genetic aberrations in key genes of the PI3K pathway regulate the composition and functional state of the immune landscape, and whether this influences the clinical benefit of immunomodulatory strategies in ILC patients. To dissect the immune regulatory mechanisms of distinct PI3K alterations we have used transgenic ILC mouse models, in which immune profiling studies by flow cytometry and immunohistochemistry revealed that distinct PI3K alterations in cancer cells differentially affect the tumor immune landscape. With some mutations driving a myeloid-rich tumor microenvironment, whereas the immune landscape of tumors harboring other PI3K mutations is dominated by lymphoid cells. To understand the observed cancer genotype-immunophenotypes mechanistically, we have performed single-cell RNA sequencing and secretome analysis to assess cellular communication between the cancer cells and the immune system. We identified key differences in ligand-receptor interactions and secreted signaling that can explain the influx of different immunosuppressive immune cell types in the tumor microenvironment of murine ILCs. We are currently investigating whether therapeutic targeting of immunosuppression is a feasible strategy for PI3K-altered ILC tumors with a tumor-promoting immune landscape. Shedding light on the mechanisms that govern the diversity and function of immune cells in the tumor microenvironment will provide a greater understanding of interpatient heterogeneity, and will pave the way for the development of novel and more tailored immunomodulatory strategies for ILC patients. Citation Format: Antoinette van Weverwijk, Michael Schubert, Joseph Siefert, Martine van Miltenburg, Kim Vrijland, Julia Houthuijzen, Anne Stunnenberg, Cheei-Sing Hau, Lodewyk Wessels, Jos Jonkers, Karin E de Visser. Dissecting the immune regulatory mechanisms of distinct PI3K alterations in invasive lobular carcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A052.

Construction of immune score and its prognostic value in invasive lobular carcinoma of the breast using computational pathology analysis.

Previous studies have shown that high level of TILs in invasive lobular carcinoma (ILC) is associated with poor prognosis, contrary to that in TNBC and HER2-positive breast cancer. The densities of six immune cell markers and three immune checkpoints in the ILC microenvironment were detected by computational pathology analysis. Then, the LASSO cox regression model was used to construct an immune score (IS) and further evaluate its prognostic value. In our ILC cohort, the low density of CD4, CD8, CD20, CD56, CD68, FOXP3, PD-1, and PD-L1 had significantly longer disease-free survival (DFS) and overall survival (OS); however, the low density of CTLA-4 was associated with shorter DFS and OS. Based on this, an IS was constructed, and patients with low-IS had significantly prolonged DFS (p < 0.0001) and OS (p < 0.0001). Multivariate analysis revealed that IS was an independent prognostic indicator for DFS and OS. Further analysis showed that IS may increase the prognostic value of TNM stage. We further explored the prognostic role of CD68 and FOXP3 in the transcriptional level and the corresponding ISm in the METABRIC dataset, and found that low proportion of CD68 and FOXP3 and their ISm were associated with longer OS, and ISm was also an independent prognostic factor for OS. IS was a promising biomarker to distinguish the prognosis in ILC patients.

Is Choosing Wisely Wise for Lobular Carcinoma in Patients Over 70Years of Age? A National Cancer Database Analysis of Sentinel Node Practice Patterns.

Controversy continues in the treatment of breast cancer in women over 70 years of age. In 2016, the Society of Surgical Oncology recommended against routine use of sentinel lymph node biopsy (SLNBx) as part of the 'Choosing Wisely Campaign'. This study examines the oncologic safety of avoidance of routine SLNBx in patients over 70 years of age with invasive lobular carcinoma (ILC). The National Cancer Database was used to identify women with invasive ductal carcinoma (IDC) and ILC diagnosed between 2012 and 2020. Clinical and pathological staging, axillary staging, surgery type, and lymph node positivity between patients with IDC or ILC were compared. Among women with T1 tumors, 85,949 (79.6%) patients with IDC and 12,761 (81.5%) patients with ILC underwent SLNBx (p < 0.001). Among patients who underwent SLNBx, those with IDC were more likely to have positive nodes (n=7535, 8.8%) than those with ILC (n=1041, 8.2%; p=0.02). During the time interval of interest, for both IDC and ILC patients, the rate of axillary lymph node dissection decreased and rates of SLNBx or no axillary staging increased. On multivariate analysis, ILC histology was associated with use of SLNBx, but without nodal positivity. A trend de-escalation of axillary staging was identified in this study, however the majority of patients meeting the 'Choosing Wisely' criteria are still undergoing SLNBx. No increased risk of nodal positivity was identified among patients with ILC, suggesting that surgeons can continue to choose wisely and limit the use of SLNBx in women over 70 years of age with T1 ILC tumors.

Optimized Modeling of Metastatic Triple-Negative Invasive Lobular Breast Carcinoma.

Invasive lobular carcinoma (ILC) is a common breast cancer subtype that is often diagnosed at advanced stages and causes significant morbidity. Late-onset secondary tumor recurrence affects up to 30% of ILC patients, posing a therapeutic challenge if resistance to systemic therapy develops. Nonetheless, there is a lack of preclinical models for ILC, and the current models do not accurately reproduce the complete range of the disease. We created clinically relevant metastatic xenografts to address this gap by grafting the triple-negative IPH-926 cell line into mouse milk ducts. The resulting intraductal xenografts accurately recapitulate lobular carcinoma in situ (LCIS), invasive lobular carcinoma, and metastatic ILC in relevant organs. Using a panel of 15 clinical markers, we characterized the intratumoral heterogeneity of primary and metastatic lesions. Interestingly, intraductal IPH-926 xenografts express low but actionable HER2 and are not dependent on supplementation with the ovarian hormone estradiol for their growth. This model provides a valuable tool to test the efficiency of potential new ILC therapeutics, and it may help detect vulnerabilities within ILC that can be exploited for therapeutic targeting.

53 The development of a multi-institutional prospective registry for patients with metastatic invasive lobular carcinoma: identifying new markers of disease progression

OBJECTIVES/GOALS: We are launching a multi-center prospective registry for patients with metastatic invasive lobular carcinoma (ILC), the second most common type of breast cancer, to better understand patterns of progression, imaging features of metastatic sites, and if serial cell free DNA measurements can serve as a surrogate marker of disease progression. METHODS/STUDY POPULATION: Patients with biopsy proven metastatic ILC of any receptor subtype will be included in the registry. We will exclude patients with ductal histology only or those with multiple primary malignancies. Patients will be enrolled at four large academic medical centers across the country. Cell free DNA measurements using a tumor informed assay will be obtained every 3 months concurrent with regular clinical imaging. Disease status will be determined by the patient’s medical oncologist by taking into account imaging, tumor markers, symptoms, and cell free DNA measurement. At each time point, patients will be surveyed on their quality of life and their medical oncologists will be asked to rate the clinical utility of the cell free DNA value. Patients will be followed indefinitely. RESULTS/ANTICIPATED RESULTS: We will explore whether the use of serial cell free DNA or a combination of blood-based biomarkers and clinical endpoints can reliably identify treatment response and disease progression in patients with metastatic ILC. Many patients with metastatic ILC have unmeasurable disease on imaging and are thereby excluded from clinical trials. The end goal of this registry is to determine if blood-based biomarkers can be used as a proxy for measurable disease in ILC patients and therefore increase clinical trial enrollment for this subgroup of patients. DISCUSSION/SIGNIFICANCE: The creation of this prospective registry will open the door for future studies of blood-based markers that reflect disease stability and progression, which is an unmet need specifically in ILC. Identification of such markers could lead to a novel treatment response endpoint, changing the way patients are enrolled in trials and managed clinically.

Comprehensive proteome, phosphoproteome and kinome characterization of luminal A breast cancer.

Breast cancer is one of the most frequently occurring malignant cancers worldwide. Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are the two most common histological subtypes of breast cancer. In this study, we aimed to deeply explore molecular characteristics and the relationship between IDC and ILC subtypes in luminal A subgroup of breast cancer using comprehensive proteomics and phosphoproteomics analysis. Cancer tissues and noncancerous adjacent tissues (NATs) with the luminal A subtype (ER- and PR-positive, HER2-negative) were obtained from paired IDC and ILC patients respectively. Label-free quantitative proteomics and phosphoproteomics methods were used to detect differential proteins and the phosphorylation status between 10 paired breast cancer and NATs. Then, the difference in protein expression and its phosphorylation between IDC and ILC subtypes were explored. Meanwhile, the activation of kinases and their substrates was also revealed by Kinase-Substrate Enrichment Analysis (KSEA). In the luminal A breast cancer, a total of 5,044 high-confidence proteins and 3,808 phosphoproteins were identified from 10 paired tissues. The protein phosphorylation level in ILC tissues was higher than that in IDC tissues. Histone H1.10 was significantly increased in IDC but decreased in ILC, Conversely, complement C4-B and Crk-like protein were significantly decreased in IDC but increased in ILC. Moreover, the increased protein expression of Septin-2, Septin-9, Heterogeneous nuclear ribonucleoprotein A1 and Kinectin but reduce of their phosphorylation could clearly distinguish IDC from ILC. In addition, IDC was primarily related to energy metabolism and MAPK pathway, while ILC was more closely involved in the AMPK and p53/p21 pathways. Furthermore, the kinomes in IDC were primarily significantly activated in the CMGC groups. Our research provides insights into the molecular characterization of IDC and ILC and contributes to discovering novel targets for further drug development and targeted treatment.

Abstract P2-03-13: Breast Cancer Index (BCI) identifies fewer patients with high risk of late recurrence and high likelihood of benefit from extended endocrine therapy with invasive lobular compared to invasive ductal carcinoma

Abstract Background: Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are the first and second most common histologic subtypes of breast cancer. Both IDC and ILC present distinguishing clinicopathologic features that contribute to differences in response to treatment and long-term prognosis. BCI is a validated gene expression assay that provides the risk of overall (0-10y) and late (5-10y) distant recurrence (DR) and predicts the likelihood of benefit from extended endocrine therapy (EET). In this analysis, BCI results between groups of HR+ ILC and IDC breast cancer patients were compared. Methods: The BCI Clinical Database for Correlative Studies is an IRB-approved de-identified database containing &amp;gt;50 clinicopathologic and molecular variables from cases submitted for BCI testing in clinical practice (N=19,126). Molecular variables include BCI Prognostic score, HOXB13/IL17BR ratio (H/I), and molecular grade index (MGI). Clinicopathologic variables were abstracted from pathology reports when available. Chi-squared tests and Kruskal-Wallis tests were used to compare categorical and numeric factors, respectively, between IDC and ILC subgroups. Kaplan-Meier survival analysis and Cox proportional hazards regression were used to analyze BCI Predictive performance in the lobular patients from IDEAL study. Results: The current study included 3814 patients submitted for BCI testing during years 4-7 post-diagnosis with available histologic subtype data (80.5% IDC; 13.2% ILC; 3.0% mixed; 3.3% other). Among those with either ductal (n=3072) or lobular (n=504) carcinomas (71% node-negative and 29% node-positive), patients with ILC were older compared to IDC (&amp;gt;70 y: 17% vs 12%). Clinically, ILC was generally less aggressive than IDC (Grade 3: 7% vs 21%; lymphovascular invasion: 9% vs 20%; HER2+: 2% vs 13%; Ki67 % positive stained cells: 29% vs 46%; p&amp;lt; 0.001 for all comparisons), with the exception that ILC had larger tumors than IDC (T2/T3: 46% vs 24%) due to its unique histology. This was consistent with BCI Prognostic results showing fewer ILC patients at high risk for late DR compared to IDC (43% vs 55%, p&amp;lt; 0.001). BCI (H/I) showed a similar trend with fewer patients with High Likelihood to benefit from EET (39% vs 43%) although the difference was not statistically significant (p=0.169). The combination of BCI prognostic and predictive results revealed that more ILC patients were classified as Low Risk/Low Likelihood of benefit (43% vs 38%) and fewer were called High Risk/High Likelihood of benefit (25% vs 35%) (p&amp;lt; 0.001) compared to IDC. The IDEAL BCI translational study included 142 ILC patients with 9.3 years of median follow-up. Similar to the BCI Clinical Database results, ILC was associated with less aggressive disease than IDC (Grade 3: 18% vs 41%; HER2+: 11% vs 24%). 39% and 61% of ILC patients were classified as BCI (H/I)-High and -Low, respectively. Given the small sample size, BCI (H/I)-High showed a non-significant absolute benefit of 11.9% (HR=0.44, 95% CI 0.09-2.14; p=0.298) and BCI (H/I)-Low showed no benefit (HR=2.63, 95% CI 0.70-9.93; p=0.138). An analysis of the 3-way interaction among treatment, biomarker and histology showed a non-significant p-value of 0.28, suggesting BCI (H/I) provides similar predictive information in ILC as in the overall population. Conclusion: BCI identified a smaller proportion of patients with ILC at High Risk of late DR and High Likelihood of benefit from EET compared to IDC. Data from the IDEAL translational study showed that while fewer patients with ILC were identified as BCI (H/I)-High, they still derived similar absolute benefit compared to the overall cohort, while those classified as BCI (H/I)-Low derived no benefit from EET. Citation Format: Otto Metzger, Neeta Parimi, Natalia Siuliukina, Yi Zhang, Kai Treuner, Gerrit-Jan Liefers. Breast Cancer Index (BCI) identifies fewer patients with high risk of late recurrence and high likelihood of benefit from extended endocrine therapy with invasive lobular compared to invasive ductal carcinoma [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 P2-03-13.

Abstract P4-03-11: Population-based survival outcomes of pure vs mixed invasive lobular breast carcinoma in Ontario, Canada

Abstract Purpose: We aim to determine incidence and survival rates of pure vs mixed invasive lobular breast carcinoma between 1990 and 2020 in the province of Ontario, Canada. We further evaluated patient and tumour factors that predict survival for invasive lobular carcinoma (ILC). Methods: Using population-based administrative healthcare datasets at Institute of Clinical Evaluative Sciences (ICES) Ontario, we calculated the crude 5-year incidence rates of pure ILC versus invasive ductal carcinoma (IDC) versus mixed ILC-IDC in the province of Ontario, Canada between 1990 and 2020. Kaplan-Meier survival curves were generated to determine the 5-, 10-, 15- and 20-year survival for ILC (and mixed ILC-IDC) as compared with IDC. Survival curves were compared using the log-rank test and stratified by stage. Using a multivariable Cox proportional hazards regression analysis, we identified patient (e.g. demographic, geographic, socioeconomic) and tumour (grade, stage, receptor subtype) factors that predicted survival for patients with ILC. Statistical analysis was performed using SAS® and P values &amp;lt; 0.05 were considered statistically significant. Results: We identified 18,551 (8%) pure ILC, 10,234 (4%) mixed ILC-IDC and 192,371 (81%) IDC cases. The crude incidence of pure ILC increased from 55.7 per 100,000 in 1990 to 80.2 per 100,000 in 2020. The crude incidence of mixed ILC-IDC peaked in the mid-2000s at 48.6 per 100,000 and subsequently declined to 32.1 per 100,000 in 2020. There was a significant difference in overall survival between the three breast cancer subtypes. Over a 30-year follow-up period (mean 9.3 +/- 7.3 years), overall survival of mixed ILC-IDC mirrors the survival of pure IDC, while women with pure ILC have inferior survival compared with IDC beginning after 10 years of follow-up (P &amp;lt; .001). The 20-year overall survival was 40% for ILC and 50% for IDC and mixed ILC-IDC. Older age &amp;gt; 55 years (vs. 50-54 years, P &amp;lt; .0001), lowest neighborhood income quintile (HR 1.1, P = .038), geographic location within Ontario (P &amp;lt; .01) and increasing Elixhauser Comorbidity Index score (P &amp;lt; .0001) predicted worse overall survival for ILC patients. Conversely, the increasing number of mammograms received in the five years prior to diagnosis predicted better overall survival (P &amp;lt; .0001). When stratified by cancer stage, the worse survival in ILC (compared with IDC and mixed ILC-IDC) was only observed for stage III patients (P = .01). Stage III and IV disease, grade 3 histology and ER/PR negativity predicted worse survival (P &amp;lt; .01). Conclusion: The crude incidence of ILC is increasing over time. Over a 30-year follow-up period (mean 9.3 +/- 7.3 years), ILC had worse overall survival compared with IDC and mixed ILC-IDC, particular stage III patients. Patient demographic and tumour factors predict overall survival in ILC. While treatment paradigms for ILC mirror that for IDC, our data demonstrates worse overall survival for ILC and a need for more research and treatments focused on improving long-term survival for ILC patients. Citation Format: David Lim, Vasily Giannakeas, Steven Narod, Kelly Metcalfe. Population-based survival outcomes of pure vs mixed invasive lobular breast carcinoma in Ontario, Canada [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 P4-03-11.

Abstract ED4-4: Lobular/pleomorphic Breast Cancer

Abstract Invasive lobular carcinoma (ILC) accounts for up to 15% of all invasive breast cancers. The general marker to identify lobular cancer is the loss or low expression of E-cadherin which is the result of genetic alterations of the E-cadherin gene which accounts for about 95%. The majority of classical ILCs are of low grade and express both hormone receptors strongly and rarely any HER2. Those not expressing the hormone-receptors are categorised as apocrine breast cancers which is a small group. Recently it has been shown that ILC is a breast cancer type which has unique genomic features. Desmedt and colleagues genomically profiled 430 ILCs, to characterize the genomic alterations present in these tumors compared to invasive ductal carcinoma (now cold unfortunately NST non-specific subtype). The most frequent altered gene was CDH1 which results in a mRNA or protein loss of the cell adhesion molecule E-cadherin. Amongst the genes found to be altered at a high frequency are ESR1 and PIK3CA/PTEN. Currently those have little or no clinical impact in early breast cancer there might be consequences for metastatic breast cancer. The molecular alterations result in a less cohesive tissue connection and influence imaging as well as surgical procedures and in the end the prognosis in those patients. The size and extend of ILC is often underestimated by imaging and clinical examination. MRI thought to be the optimal imaging turned out to have no influence on positive margins and is no longer considered standard for all ILCs. Several data suggest that ILCs have an improved outcome the first 5 years after primary diagnosis but thereafter the survival curves in general lie below those for non lobular breast cancer. ILC has a distinct metastatic pattern and often metastasise into the GI tract and the ovaries and less frequently to the lung. Breast conserving surgery as well as mastectomy can be used when indicated based on tumor size and patients preference. Because ILC more often presents at higher stage, mastectomy is more frequently performed. But even after neoadjuvant chemotherapy we could demonstrate, despite response even resulting in pCR, mastectomy was more frequently conducted in ILC patients compared to non-ILC. In this analysis 71% of the non-ILC did receive BCS compared to only 59% in ILC (p Systemic therapy follows the general recommendations based on stage and histopathological profile. Neoadjuvant chemotherapy results in significantly lower rates of pathological responses. All analyses showed response rate in single digit numbers (far below 10%) but the less classical ILCs with either grade 3 or hormone-receptor negativity have a higher chance of achieving a pCR. Those ILCs with grade 3 and hormone-receptor negativity (apocrine cancer) have a pCR rate comparable to invasive ductal carcinoma (IDC). It is not surprising that lobular breast cancer does not respond as well as IDC to neoadjuvant chemotherapy because their biological features are, as described above, more luminal A like (high hormone receptor positivity, low grade, low proliferation). Because many patients with ILC present with extended diseases, they might still benefit from neoadjuvant chemotherapy even if they do not achieve a pathologic complete response, downstaging is an option and would potentially lead to less mastectomies. Because of the luminal A like type of the majority of ILCs endocrine therapy seems to be the treatment of choice. Some data even suggested a better outcome for ILC breast cancer when treated with an aromatase inhibitor compared to tamoxifen. But other data are controversial in this regard and did not confirm the data from BIG 1-98. In conclusion the molecular profile of ILC seems to be distinct but does not result in different treatment paradigms. We should not underestimate the necessity of optimal treatment, including chemotherapy for invasive lobular breast cancer patients. Citation Format: Sibylle Loibl. Lobular/pleomorphic 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 ED4-4.

Descriptive Study and Surgical Management Among Infiltrating Lobular Carcinoma Patients Admitted to King Abdulaziz Medical City From 2000 to 2017: A Retrospective Cross-Sectional Study.

Invasive lobular carcinoma (ILC) is the second most common histologic type of breast carcinoma. The etiology of ILC is unknown; however, many contributing risk factors have been suggested. Treatment of ILC can be divided into local and systemic. Our objectives were toassess the clinical presentations, risk factors, radiological findings, pathological types, and surgical options for patients with ILC treated at the national guard hospital. Identify the factors associated with metastasis and recurrence. Retrospective cross-sectional descriptive study at a tertiary care center in Riyadh.All adultpatients aged 16 years and above, from different nationalities, and both genders, were diagnosed with ILC from 2000 to 2017 and followed up at KAMC. The sampling technique was a non-probability consecutive technique.Among 1066 patients identified, 91 patients were diagnosed with ILC over seventeen years study period. The median age at the primary diagnosis was 50. On the clinical examination, 63 (71%) cases were found to have palpable masses which was the most suspicious finding. On radiology, the most encountered finding was speculated masses which were seen in 76 (84%). Regarding the pathology, unilateral breast cancer was seen in 82 while bilateral breast cancer was found only in eight. For the biopsy, a core needle biopsy was the most commonly used in 83 (91%) patients. The most documented surgery for ILC patients was a modified radical mastectomy. Metastasis in different organs was identified with the musculoskeletal system being the commonest site. Different significant variables were compared between patients with or without metastasis. Skin changes, post-operative invasion, estrogen, progesterone, and HER2 receptors were significantly associated with metastasis. Patients with metastasis were less likely to have conservative surgery. Regarding the Recurrence and five years survival, out of 62 cases, 10 had recurrence within five years, which was more prevalent in patients who had fine needle aspiration, excisional biopsy, and nulliparous patients. To our knowledge, this is the first study to exclusively describeILC in Saudi Arabia. The results of this current study are highly important, as these results provide baseline data of ILC in the capital city of Saudi Arabia.