Invasive Lobular Breast Cancer Research Articles

Abstract PO4-02-04: Overall survival and disease recurrence rates in patients with invasive lobular breast cancer of the PenelopeB cohort

Abstract Background: In the PENELOPEB trial, the addition of 1-year of cyclin-dependent kinase 4/6 (CDK4/6) inhibitor palbociclib to standard endocrine therapy (ET) for women with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) early breast cancer at high risk of recurrence after neoadjuvant chemotherapy (NACT) did not improve invasive disease-free survival (iDFS) or overall survival (OS) in the main study analysis. Invasive lobular breast cancer (ILC) accounts for ~15% of all breast cancers (BC) and represents an underinvestigated subtype of BC with typically less sensitivity to (neo)adjuvant chemotherapy, and poor distant disease-free survival (DDFS) irrespective of response to NACT. Here, we report the post-hoc analysis results of iDFS, DDFS and OS in pre- and postmenopausal women enrolled on PENELOPEB and with ILC. Methods: Patients with HR+/HER2-negative BC without pathological complete response (pCR) after taxane-containing NACT and at high risk of relapse (CPS-EG score ≥3, or 2 and ypN+) were randomized (1:1) to receive 13 cycles of palbociclib 125mg daily or placebo on days 1-21 of a 28-day cycle in addition to standard ET with tamoxifen (TAM) +/- gonadotropin-releasing hormone analogue (GnRHa) or aromatase inhibitor (AI) +/- GnRH. Randomization was stratified by nodal status at surgery, age at first diagnosis (< 50 vs. ≥50 years), Ki-67, region, and CPS-EG score. ILC diagnosis was locally assessed and reported by the investigators on the pathology case report form. The primary objective of this post-hoc analysis was to evaluate iDFS, DDFS and OS by treatment arm in patients with high risk ILC. Results: A total of 1,250 patients were randomized, of whom 110 had ILC and were nearly uniformly distributed between both treatment arms (palbociclib n=58 vs. placebo n=52), with a higher proportion of postmenopausal women (58.6% in the palbociclib arm vs. 53.8% in the placebo arm) compared to premenopausal women (41.4% in the palbociclib arm vs. 46.2% in placebo arm). There was no difference in the distribution of AI/TAM use between the treatment arms. An estimated absolute 3-year-iDFS difference of 18.3% with palbociclib compared to placebo (iDFS 88.4% [95% CI 76.0-94.6] vs. 70.1% [95% CI 55.3-80.7]) with a HR of 0.66 [95% CI 0.27 – 1.61, log-rank p=0.354]) was observed. A comparable 3-year-DDFS difference of 16.3% was observed. An estimated 3-year-OS difference of 16.4% (98.0% [95% CI 86.6 – 99.7] vs. 81.6% [95% CI 67.5 – 90.0]) with a hazard ratio (HR) of 0.27 (95% CI 0.05 – 1.43, log-rank p=0.108) was observed. Out of 12 observed deaths (n=2 palbociclib vs. n=10 placebo), 11 (in placebo arm) were related to metastasic BC. Conclusions: In this post-hoc analysis, a trend towards improvement in OS and a trend in favor of iDFS and DDFS for the addition of palbociclib to ET was observed among women with HR+/HER2- ILC at high risk of recurrence after NACT, but these differences were not statistically significant. This could represent a valuable treatment option for patients with high risk ILC. Due to the small sample size of the ILC subgroup, further follow-up evaluation is necessary. Moreover, analyses in the ILC subgroup from other adjuvant CDK4/6 inhibitor trials could substantiate these findings. Table. Overall survival and disease recurrence rates in patients with invasive lobular breast cancer of the PenelopeB cohort Results of iDFS, DDFS and OS. Citation Format: Hervé Bonnefoi, Frederik Marmé, Miguel Martín, Michael Untch, Sung-Bae Kim, Harry Bear, Nicole McCarthy, Karen Gelmon, José Ángel García-Sáenz, Catherine M. Kelly, Toralf Reimer, Zhe Zhang, Masakazu Toi, Hope Rugo, Michael Gnant, Andreas Makris, Nader Hirmas, Valentina Nekljudova, Johannes Holtschmidt, Sibylle Loibl. Overall survival and disease recurrence rates in patients with invasive lobular breast cancer of the PenelopeB cohort [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 PO4-02-04.

Abstract ED02-01: Biological peculiarities of ILC

Abstract One in 8 women will be diagnosed with breast cancer in her lifetime and approximately 15% of them have invasive lobular breast cancer (ILC). ILC differs in many ways from the most common BC subtype, called non-special type (NST) (Van Baelen et al. Ann Oncol 2022). The microscopic hallmark of ILC is the presence of single files of relatively small discohesive tumor cells, which stems from a dysfunctional E-cadherin-catenins complex at the intercellular junctions, a feature that is uncommon in NST. More than 90% of ILC express the estrogen (ER) and/or progesterone receptor (PR) and lack HER2 amplification, while this is only the case in ~65% of NST. Patients with ILC also show a distinct clinical behavior as compared to NST: generally, a poor response to chemotherapy, more late recurrences, and a peculiar metastatic pattern. The first part of the presentation will focus on presenting the biological knowledge we have accumulated over the years about primary ILC. We will review the studies which compared ILC and NST at the genomic, transcriptomic and immune level. The second part of the presentation will be focused on metastatic breast cancer. Here we will review the published evidence regarding the metastatic dissemination of ILC, its genomic landscape and the contribution of the local tumor microenvironment. We will also dedicate attention to the important biological and clinical knowledge which can be gained by studying samples collected from patients with metastatic ILC who consented to post-mortem tissue donation. Finally, the last part of the presentation will be dedicated to mixed NST/ILC tumors. These tumors account for up to 18% of all invasive breast cancers and represent an even more under investigated area of research as pure ILC. Citation Format: C. Desmedt. Biological peculiarities of ILC [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 ED02-01.

Abstract PO2-27-08: Discovery of glucocorticoid receptor-induced EMT and integrin gene expression and increased cell motility in invasive lobular breast cancer

Abstract Estrogen receptor (ER)-positive, invasive lobular carcinoma (ILC) is the second most common histological subtype of breast cancer. Although the five-year stage-matched survival is improved compared to infiltrating ductal carcinoma (IDC), ILC late metastatic recurrences ( >5 years) are more frequent. Understanding the molecular mechanisms of lobular breast cancer’s significantly dormant yet ultimately metastatic phenotype is important to improve clinical outcomes. Our laboratory had previously shown that GR activation in ER+ IDC was associated with decreased cell proliferation, but little is known about GR activity in ER+ ILC. By examining gene expression following GR activation in metastases-derived ER+/GR+ human ILC cell lines, we recently uncovered that GR-activation increases EMT and integrin pathways. Here we show for the first time that in addition to activation of these gene expression pathways, GR activation increases ILC cellular migration in microchannels coated with collagen and fibronectin, consistent with a potential for GR activation to increase ILC metastases. We examined GR expression and activation in SUM44 GR+/GR-, and BCK4 GR+/GR- and MM134 GR+ cell lines and will present data comparing gene GR- mediated expression in the presence of cortisol and clinically relevant GR modulation. Ongoing investigations also include in vivo MIND modeling with GR modulation. Citation Format: Baylee Porter, Candace Frerich, Muriel Laine, Sunati Sahoo, Geoffrey Greene, Jeon Lee, Lynda Bennett, Suzanne Conzen. Discovery of glucocorticoid receptor-induced EMT and integrin gene expression and increased cell motility in invasive lobular breast cancer [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 PO2-27-08.

Abstract PO5-20-10: Treatment with CDK4/6 Inhibitor in a Patient with Metastatic Breast Cancer Causing Myelophthisis

Abstract Background: Symptomatic bone marrow metastasis causing myelophthisis is a rare manifestation of metastatic breast cancer, indicating a poor prognosis due to significant cytopenias. CDK4/6 inhibitors are first-line therapies for metastatic hormone-positive breast cancer but remain an unclear choice in breast cancer patients with significant cytopenias due to associated hematological adverse effects. We present a case of biopsy-proven hormone-positive breast cancer with bone marrow infiltration causing profound pancytopenia. CDK4/6 inhibitors were safely administered despite their cytopenic effects. Case Presentation: A 59-year-old female presented after an abnormal annual mammogram and biopsy showed calcifications stromal fibrosis, cyst formation, and usual ductal hyperplasia in the right upper outer quadrant. One month later, she presented to an outside hospital with gingival bleeding, epistaxis, progressive dyspnea on exertion, and generalized weakness. Labs showed severe anemia with a hemoglobin of 4.8 g/dL (baseline 12.1 g/dL), thrombocytopenia with platelets of 5 K/mm (baseline 215 K/mm), LDH of 879, reticulocyte count of 5%, and negative direct Coombs test. Peripheral smear showed no schistocytes, but showed nucleated RBCs, severely reduced platelets, and occasional giant platelets. The patient was treated for presumed ITP, and the presence of nucleated RBCs prompted bone marrow biopsy which confirmed metastatic invasive lobular carcinoma breast cancer (ER 90-95%, PR 90-95%, HER2 1+). She was discharged on letrozole 2.5 mg daily with close outpatient oncologic follow-up. One week later, she presented to our institution with persistent symptomatic anemia and thrombocytopenia. Inpatient systemic therapy was begun using dose-reduced Palbociclib (75mg) and letrozole with close CBC monitoring while also receiving packed red blood cells (goal >6.5) and platelet transfusions (goal >10). Repeat bone marrow biopsy showed extensive marrow fibrosis, but no significant hematopoietic elements. ADAMTS13 was 134%, ruling out TTP, and she was treated again for presumed ITP with dexamethasone and IVIG, Throughout the 4-week admission, her right breast mass decreased in size and she was discharged after completing 3 weeks of Palbociclib with biweekly outpatient transfusions. During follow-up, the patient’s hemoglobin and platelets slowly started to respond allowing her to become transfusion-independent and allowing dose escalation. Restaging scans 2 months after hospitalization showed an overall improvement of disease burden. The patient continued to do well for almost 18 months, however, later redeveloped visceral crisis and is responding to chemotherapy. Discussion: There is limited data on the management of breast cancer with bone marrow infiltration at presentation. A wide range of survival data in different case reports exists, ranging from 5 to 44 months. However, chemotherapy was used in these studies rather than CDK4/6 inhibitors. By far, cytopenias are the most concerning grade 3 and 4 side effect of Palbociclib. Data from the PALOMA-1 trial suggest that hematologic toxicities, specifically neutropenia, were different from those associated with cytotoxic chemotherapies and are more transient and reversible in nature. Studies have examined the in vitro mechanism of bone marrow suppression in Palbociclib versus cytotoxic chemotherapy, and its cytostatic effect on neutrophil precursors allows for hematological toxicities to be transient. With strong supportive care measures, patients in bone marrow visceral crisis can be safely treated with cytopenic CDK4/6 inhibitors. Citation Format: Nikita Dahake, Jordan Senchak, Jalil Nasibli, Jason Incorvati. Treatment with CDK4/6 Inhibitor in a Patient with Metastatic Breast Cancer Causing Myelophthisis [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 PO5-20-10.

Abstract PO5-08-07: Ki-67 Expression in Breast Cancer associated with ATM, BRCA1, BRCA2, CHEK2 and PALB2 Pathogenic Variants

Abstract Background: Germline Pathogenic Variants (PVs) in ATM, BRCA1, BRCA2, CHEK2, and PALB2 are known to increase breast cancer (BCa) risk, but the effect of these PVs on tumor biology is not well-understood. Ki-67 is an established prognostic marker in hormone receptor (HR) positive breast cancer but the distribution of Ki-67 in breast cancer associated with germline PVs is not known. Methods: The study included patients with loco-regional (Stage I-III) HR-positive (ER+ or PR+), HER2-negative invasive ductal or lobular breast cancer evaluated at Mayo Clinic for curative intent treatment between 2012 and 2021. PV carrier status was ascertained in more than two-thirds of cases from germline whole exome sequencing (Regeneron) of patients who participated in a prospective registry at Mayo Clinic. Additional PV carriers were identified through a review of the results of clinical germline genetic testing in electronic medical records aided by natural language processing. Clinically performed Ki-67 values were abstracted from electronic medical records and analyzed as continuous and categorical variables (low: < 20% vs. high: ≥20%). Throughout the timeline of the study, a consistent method for assessment of Ki-67 was utilized at Mayo Clinic, Rochester: Immunohistochemical staining of the Ki-67 antigen in formalin-fixed paraffin-embedded tissue was performed using MIB-1 clone, the scanned slides were reviewed by a technologist and traced areas further analyzed for Ki-67 using Aperio Software. Patients who received neoadjuvant therapy prior to the assessment of Ki-67, with metastatic disease at diagnosis, with PVs in two or more genes of interest, or unknown germline PV or Ki-67 status were excluded from the analysis. Multiple primary tumors in the same patient diagnosed within one year of each other were analyzed independently. The control (non-carrier) group included randomly selected patients from the prospective registry who tested negative for PVs in the five genes over the same time period. Ki-67 values were compared between germline PV carriers and non-carriers in a multivariable logistic regression analysis adjusting for sex, race, age at diagnosis, stage at presentation, and histology of the tumor. Results: A total of 113 HR+/HER2- tumors from 111 PV carriers (ATM: 27, BRCA1: 24, BRCA2: 28, CHEK2: 22, and PALB2:12) along with 431 HR+/HER2- tumors from 422 randomly selected non-carriers were evaluated. The majority (>95%) of patients were non-Hispanic White. Germline PV carriers in each gene were diagnosed at a significantly younger age (P< 0.05) compared to non-carriers. The median Ki-67 value was 12 (Range: 1 to 93) for non-carriers, 16 (Range: 0 to 79) for ATM, 31 (Range: 4 to 86) for BRCA1, 30 (Range: 6 to 80) for BRCA2, 13 (Range: 1 to 38) for CHEK2, and 20 (Range: 3 to 46) for PALB2 PV carriers. In multivariable analysis, compared to non-carriers, we observed significantly higher odds of a high Ki67 value (≥20%) for tumors arising from germline PV carriers in BRCA1 (Odds Ratio (OR): 7.3, 95%CI: 2.3 – 23.3, p< 0.001), BRCA2 (OR: 3.0, 95%CI: 1.2 – 7.4, p=0.02) and PALB2 (OR: 3.9, 95%CI: 1.1 – 14.5, p=0.04). No such relationship was observed with either ATM (OR: 1.1, 95%CI: 0.4 – 2.9, p=0.81) or CHEK2 (OR: 0.8, 95%CI: 0.3 – 2.2, p=0.63). Conclusion: This study reveals that HR+/HER2- tumors in BRCA1, BRCA2, and PALB2 PV carriers have a significantly higher Ki-67 expression compared to non-carriers. These findings have implications for understanding prognosis and endocrine response PV with HR+ breast cancer. Further exploration of the relationships between Ki67 and germline PV status is necessary to personalize systemic therapy options in germline PV carriers. Acknowledgments: Thank you to Regeneron Genetics Center. The study was funded in part by the NIH Specialized Program of Research Excellence in Breast Cancer [P50CA116201] to Mayo Clinic, Mayo Clinic Department of Oncology Small Grants Program, and the Paul Calabresi Program at Mayo Clinic Citation Format: Robert Scheel, Grace Choong, Tara Rao, Nicholas Boddicker, Chunling Hu, Jie Na, Vinod Kaggal, Sean Murphy, Karthik Giridhar, Saba Yasir, Matthew Goetz, Fergus Couch, Siddhartha Yadav. Ki-67 Expression in Breast Cancer associated with ATM, BRCA1, BRCA2, CHEK2 and PALB2 Pathogenic Variants [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 PO5-08-07.

Abstract PO3-13-10: Proteogenomic characterization of primary invasive breast tumors from young women compared to matched tumors from older women

Abstract Introduction: Breast cancer (BC) in women < 40 years old accounts for ~5% of BC diagnosed in the U.S. However, young women have more aggressive tumors and worse outcomes, including higher rates of recurrence and lower disease-free and overall survival, compared to older women. To better understand mechanisms for these disparities, an integrated proteogenomic study of tumors from young (< 40) and older (≥ 60) women was performed through the Applied Proteogenomics OrganizationaL Learning and Outcomes (APOLLO) program. Methods: 34 pairs of retrospectively collected, untreated primary breast tumors from young and older women, matched by immunohistochemistry (IHC) subtype and race, were selected from the Clinical Breast Care Project. Median patient follow-up was 7 years. Tumor cells were enriched by laser microdissection and analyzed using RNA sequencing, whole genome sequencing, global proteomics, phosphoproteomics, and reverse phase protein array (RPPA). Molecular and clinical data from tumors from young and old patients in the TCGA-BC and METABRIC studies, matched by IHC subtype and race, were used to corroborate findings from our cohort. Results are presented comparing young women and their tumors to their older counterparts. Results: Young women have worse clinical outcome measured by progression-free interval. Despite matching for IHC subtypes, tumors from young women are enriched for intrinsic basal-like subtype, BRCA1/2 germline mutations, and had fewer invasive lobular BCs. Differentially enriched molecules and pathways: A number of significantly differentially expressed genes (DEGs) and proteins were detected, which were able to separate luminal subtypes of BC by patient age. IRS1 and IRS2 were enriched at both transcript and protein levels; IRS1 has been reported to promote tamoxifen resistance. We observed limited overlap of DEGs between the APOLLO, TCGA, and METABRIC datasets. In contrast, 14 of the 28 significantly upregulated Cancer Hallmark pathways were also enriched in TCGA-BC and METABRIC datasets; suggesting targeting pathways, vs genes, may be more effective for therapeutic intervention. Integrated pathway/network analysis: Integrated pathway analysis of RNA and protein levels identified 5 Hallmark pathways upregulated in younger women, including ER response and proliferative pathways, and 6 downregulated immune-response pathways; 10 of the 11 were supported by the public datasets. Immune scores were also lower. Kinase substrate enrichment analysis identified 4 kinases with increased activity in tumors from young women. ESR1/ER: We identified for the first time a significant reduction of ER protein expression while confirming previously reported lower ESR1 gene expression and copy number variations. Surprisingly, integrated pathway analysis identified elevation of early and late estrogen responses in young women. ER activation, indicated by phosphorylated ER (pS118) normalized to total ER protein, was elevated in LumA tumors from young women. Conclusions: This first-ever integrated proteogenomic study shows that BC in young women is enriched for more aggressive molecular subtypes and for genes that promote tamoxifen resistance, exhibits lower immune pathways and immune scores, and shows enhanced ER responses despite lower gene and protein expression of ER. These findings may contribute to the understanding of the molecular mechanisms underlying worse outcomes of BC in young women, and offer new insight to therapeutic strategies. Disclaimer: The contents of this publication are the sole responsibility of the authors and do not necessarily reflect the views, opinions or policies of USUHS, HJF, the DoD or the Departments of the Army, Navy or Air Force. Mention of trade names, commercial products, or organizations does not imply endorsement by the U.S. Government. Citation Format: Praveen Kumar Raj Kumar, Jianfang Liu, Anthony Soltis, Nicholas Bateman, Qingrong Chen, Lori Sturtz, Brenda Deyarmin, Mariaelena Pierobon, Tamara Abulez, Anupama Praveen-Kumar, Xijun Zhang, Trinh Nguyen, Chunhua Yan, Ying Hu, Kate Guion, Jeffrey Hooke, Albert Kovatich, Leigh Fantacone-Campbell, Brad Mostoller, Leonid Kvecher, Stella Somiari, Patricia Steeg, Sheila Rajagopal, Kathleen Darcy, Jerry Lee, Clifton Dalgard, Thomas Conrads, Emanuel Petricoin, Daoud Meerzaman, Matthew Wilkerson, APOLLO Research Network, Xiaoying Lin, Craig Shriver, Stanley Lipkowitz, Hai Hu. Proteogenomic characterization of primary invasive breast tumors from young women compared to matched tumors from older women [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 PO3-13-10.

Abstract PO4-28-09: Upregulation of the immune checkpoint protein B7-H3 is associated with an immune suppressive microenvironment in progression from in situ to invasive lobular breast cancer

Abstract Invasive lobular breast cancer (ILC) is an understudied subtype of breast cancer characterized by late recurrence, metastasis to serosal surfaces including the peritoneum, and poor long-term outcomes. Lobular carcinoma in situ (LCIS) is a non-obligate precursor to ILC but is associated with a 30% increased risk of developing ILC. Therefore, understanding the underlying changes that occur in the invasive lobular cells as well as their tumor microenvironment (TME) during the transition from LCIS to ILC is critical for the development of novel therapeutic targets that could be used in early disease. To address this, we used combined spatial whole genome transcriptomics and a 97-protein proteomics assay to examine the spatial molecular profiles of coexistent LCIS and ILC. PanCK-positive tumor cells and panCK-negative stromal cells were segmented and analyzed separately for both RNA and protein. Despite the close spatial proximity of LCIS and ILC, there were notable differences in gene and protein expression in the tumor cells as well as the tumor microenvironment (TME). RNA profiling revealed significant upregulation of genes encoding essential components of the extracellular matrix, including type I, 3 and 5 collagens, small leucine-rich proteoglycans byglycan (BGN) and lumican (LUM), periostin (POSTN) and secreted protein acidic and cysteine rich (SPARC). Metalloprotease genes MMP2 and MMP11 were also upregulated. Genes highly expressed in the LCIS tumor compartment were KRT5, KRT14 KRT17 and MYLK which are highly expressed in myoepithelial cells at the periphery of the LCIS. One of the most upregulated proteins in ILC cells was B7 homology 3 protein (B7-H3) or Cluster of Differentiation 276 (CD276). B7-H3 is a transmembrane immunoregulatory protein belonging to the B7 family (that also includes PD-L1 and PD-L2). This immune checkpoint protein is overexpressed in many tumors but is barely expressed in normal cells. B7-H3 has been associated with several aspects of cancer progression, such as evasion of tumor immune surveillance and metastasis, and is strongly linked to poor prognosis in cancer. Compared to the LCIS TME, B7-H3 was also the most upregulated protein in the ILC TME along with the tumor-promoting M1 macrophage marker CD68 and the regulatory T-cell marker FOXP3. The lymphocyte marker CD45 was downregulated as well as T-cell proteins CD3, CD40 and granzyme B. Moreover, CD27, a memory B-cell marker was most highly expressed in the TME surrounding LCIS compared to ILC. Overall, these molecular profiles support a transition to a toward a much more immunosuppressive environment for invasive tumor cells compared to LCIS. Based on these data, our working hypothesis is that upregulation of B7-H3 on lobular tumor cells promotes invasion allowing interaction with laminins, integrins and other ECM proteins in the basement membrane and the interstitial membrane as LCIS acquire invasive properties of ILC. Furthermore, upregulation of B7-H3 on CD3+ HLA-DR+ expressing antigen presenting cells also promotes a suppressive immune microenvironment by inhibiting T-cell proliferation and downregulating cytokine production. In sum, these strongly concurrent spatial transcriptome and protein data suggest that B7-H3 and the immune suppressive network of ILC may be a promising target for early stage lobular breast cancer. B7-H3 Inhibitors could be explored in the neoadjuvant setting to evaluate the efficacy of immunotherapy in primary ILC. Citation Format: Lynda Bennett, Sunati Sahoo, Cheryl Lewis, Indu Raman, Candace Frerich, Guanchun Chen, Min Xu, Suzanne Conzen. Upregulation of the immune checkpoint protein B7-H3 is associated with an immune suppressive microenvironment in progression from in situ to invasive lobular breast cancer [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 PO4-28-09.

Abstract PO2-07-09: Early stage invasive lobular breast cancer is underestimated on conventional imaging including MRI

Abstract Background: Invasive lobular carcinoma (ILC), representing 15% of all invasive breast cancers, is characterized by loss or dysfunction of the adhesion molecule E-cadherin. This leads to an infiltrative growth pattern that is unlikely to disrupt the normal architecture of breast tissue. As a result, ILC is often non-mass forming and imaging is limited in correctly diagnosing stage I-III ILC. Mammography is believed to underestimate ILC, while MRI tends to overestimate the extent of ILC. The aim of this retrospective study was to correlate radiological with pathological findings. Methods: All patients diagnosed with stage I-III pure (i.e. not mixed) ILC between January 2000 and December 2020 who underwent primary surgery in University Hospitals Leuven, were included. Data on patient characteristics, preoperative imaging and pathology were collected from the patient files. Imaging and pathology measurements were compared by use of Pearson correlation coefficient, Whitney U test or Chi-square test. Weighted kappa statistics were used to assess agreement. Since the techniques of mammography and ultrasound have evolved in the past 20 years, different time periods were considered in sub-analyses (2000-2004, 2005-2009, 2010-2014, 2015-2020). Results: In total 1029 patients were included. Median age at diagnosis was 61.0 years (range 32.0 – 95.0 years). The breast density score determined on mammogram was Bi-RADS type A for 52 (5.1%) patients, B for 238 (23.1%) patients, C for 235 (22.8%) patients and D for 141 (13.7%) patients. Density score was missing from the reports of the remaining patients (n=363, 35.3%). Contrast enhanced breast magnetic resonance imaging (MRI) was performed in 709 (68.9%) patients. An increase in preoperative use of MRI was seen over the years. In comparison to tumor size reported by pathology, all imaging techniques underestimated the tumor size. The mean difference in largest tumor size compared to pathology was 14.64 ± 21.15 mm for mammography, 18.19 ± 21.66 mm for ultrasound and 9.93 ± 20.63 mm for MRI. A higher breast density level and a larger tumor size were significantly associated with a larger difference between diameter on pathology versus mammography (ρ=0.102, p-value 0.025 and ρ=0.530, p-value < 0.001 respectively). Changes over different time periods are shown in Table 1 for mammography and ultrasound. There was an agreement on unifocality versus multifocality between pathology and mammography for 81.2% of the patients. In 52.1% of the 236 cases where multifocality was reported on MRI, only 1 lesion was reported by the pathologist. Multifocality was seen on pathology in 12.0% of the 460 cases that were seen as unifocal lesions on MRI. Considering adenopathies, the false positive rate of ultrasound was 3.0%. However, the false negative rate was 68.3%. Conclusions: The local extent of ILC is underestimated by conventional imaging techniques. Unlike previous reports, our results suggest that tumor size of ILC is also underestimated by MRI. Ultrasound was inferior to mammography and MRI in estimating tumor size in our series. It was confirmed that MRI tends to overestimate the number of foci which might lead to unnecessary secondary ultrasounds and biopsies. The presurgical underestimation of lymph node involvement might increase the need of secondary surgeries. It is crucial to address these limitations in imaging of ILC and to prioritize the development of enhanced imaging techniques to improve diagnostic accuracy for these patients. Table 1: difference between imaging techniques and pathology by year of diagnosis Citation Format: Kaat Van Herck, Karen Van Baelen, Chantal Van Ongeval, Valerie Celis, Helen De Boodt, Machteld Keupers, Renate Prevos, Giuseppe Floris, Ines Nevelsteen, Ann Smeets, Thaïs Baert, Sileny Han, Hans Wildiers, Annouschka Laenen, Christine Desmedt, Patrick Neven. Early stage invasive lobular breast cancer is underestimated on conventional imaging including MRI [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 PO2-07-09.

Abstract PO5-05-10: Analysis of Trends in Funding of Metastatic Breast Cancer Research

Abstract Introduction To inform funding strategies for research in metastatic breast cancer (MBC), knowledge of the current research landscape and identification of potential gap areas requiring additional research are essential. In 2014, the Metastatic Breast Cancer Alliance (MBCA) published an analysis that showed that between 2000 and 2013, only 7% of all funds for breast cancer research were devoted to metastasis. As more people are living with MBC, addressing research priorities for those living with the disease is important, as is understanding gaps in the current funding landscape of MBC research to appropriately target investment. Methods A collaborative effort between funders and patients was undertaken to analyze breast cancer projects funded between 2014 and 2020 from the International Cancer Research Partnership database, the Health Resource Alliance database, and MBCA members, representing grants from 83 non-profit organizations worldwide. Project titles, abstracts, and classifications of these grants were extracted from these databases. Next, to identify research projects in the databases that are related to metastasis, a classification tool that uses a machine learning algorithm was built, trained on manually coded grants from the 2000-2013 analysis, and validated by expert coders. Projects were then coded according to a pre-established metastasis classification policy to categories such as type of research (e.g., treatment), genes or proteins studied, site of metastasis, breast cancer subtype, and patient priority questions. In terms of the latter, MBCA members living with MBC were surveyed about research priorities. Member advocates ranked survey questions according to highest patient priority, and these were converted to language that could be queried with the tool. Results Investment in MBC research nearly doubled from 2014 to 2020. Research into understanding and overcoming treatment resistance, which was the highest patient priority question, increased from 15% in 2014 to 26% of the MBC portfolio in 2020; this was a statistically significant increase above the rate of inflation. In terms of treatment resistance according to subtype, the highest number of projects focused on triple-negative MBC (>300). By contrast, < 20 projects were focused on overcoming treatment resistance in metastatic invasive lobular breast cancer. Of the six categories evaluated (e.g. biology and detection/diagnosis/prognosis), the largest increase in investment was for treatments. Discussion The coding tool allows for ongoing complex queries such as identification of funded research relevant to areas identified as important by MBC advocates (Table) and provides a funders’ ‘dashboard’ to identify gap areas in need of further research funding. This collaborative effort between funders and patient advocates, and the resulting current and future analyses, can be used to focus advocacy efforts to drive research funding of priorities and understudied areas of MBC. Despite the increase in funding, the investment in metastatic research–the primary cause of death from breast cancer–remains insufficient. Table. Research Priorities of MBC Patient Advocates Citation Format: Margaret Flowers, Teri Pollastro, Kari Wojtanik, Katherine McKenzie, Kimberly Badovinac, Medha Deoras-Sutliff, Lynne Davies. Analysis of Trends in Funding of Metastatic Breast Cancer Research [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 PO5-05-10.

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

Invasive Lobular Carcinoma (ILC) is a morphologically distinct breast cancer subtype that represents up to 15% of all breast cancers. Compared to Invasive Breast Carcinoma of No Special Type (IBC-NST), ILCs exhibit poorer long-term outcome and a unique pattern of metastasis. Despite these differences, the systematic discovery of robust prognostic biomarkers and therapeutically actionable molecular pathways in ILC remains limited. Pathway-centric multivariable models using statistical machine learning were developed and tested in seven retrospective clinico-genomic cohorts (n = 996). Further external validation was performed using a new RNA-Seq clinical cohort of aggressive ILCs (n = 48). mRNA dysregulation scores of 25 pathways were strongly prognostic in ILC (FDR-adjusted P < 0.05). Of these, three pathways including Cell-cell communication, Innate immune system and Smooth muscle contraction were also independent predictors of chemotherapy response. To aggregate these findings, a multivariable machine learning predictor called PSILC was developed and successfully validated for predicting overall and metastasis-free survival in ILC. Integration of PSILC with CRISPR-Cas9 screening data from breast cancer cell lines revealed 16 candidate therapeutic targets that were synthetic lethal with high-risk ILCs. This study provides interpretable prognostic and predictive biomarkers of ILC which could serve as the starting points for targeted drug discovery for this disease.

Retrospective cohort study on the bilateral occurrence of invasive lobular breast cancer

ObjectiveInvasive lobular carcinoma (ILC) is the second most common histological subtype of invasive breast cancer, following the no special type (NST) invasive carcinoma. It has historically been assumed that ILC occurs bilaterally in 20–29% of cases, which has influenced the inclusion of MRI in the standard workup of ILC according to European guidelines. However, challenging this long-held belief regarding the bilateral occurrence of ILC opens up the possibility of revising the guidelines and using MRI only for more specific indications. This study aims to evaluate whether the previously reported high percentage of bilaterality still holds true and to question the added value of MRI in the standard workup of ILC. Study designA retrospective cohort study was conducted following approval from the institutional review board (EC 21/18/249) at Antwerp University Hospital (UZA). The cohort comprised female patients of all ages who had been diagnosed with either ILC or NST invasive carcinoma and had sought consultation at the UZA breast clinic. A comprehensive database was established to collect information on patient characteristics, imaging, and pathology. ResultsA total of 271 patients with ILC were included in the study, with incidence dates ranging from 01/01/2007 to 01/01/2023. Among these patients, a synchronous bilateral ILC lesion was observed in 1.85% (5/271) of cases. This proportion is significantly lower than the reported percentage of patients with a bilateral lesion in the literature population, which stands at 4.95%. The reference group consisted of 809 patients with NST invasive carcinoma, with incidence dates ranging from 01/01/2017 to 01/01/2023. In the control group, a synchronous bilateral NST lesion was observed in 3.96% (32/809) of cases. There is no significant difference in the bilaterality rates between the group of ILC patients and the group of NST patients. Furthermore, MRI did not detect any histopathologically confirmed contralateral ILC lesion that had not already been detected by mammography or ultrasound. ConclusionsThe study results indicate a lower occurrence of bilateral ILC than previously assumed. Additionally, the incidence of synchronous bilateral lesions in ILC patients is not higher compared to patients with NST invasive carcinoma. Performing an MRI does not provide additional value in detecting bilateral carcinomas in ILC. Consequently, it is recommended that the current European guidelines be reassessed, and the indications for undergoing an MRI should be adjusted accordingly.

177 (PB-084) Poster - Expanding the use of Oncoplastic Surgery in Invasive Lobular Breast Cancer: long-term results of 476 patients treated with three different surgical approaches

177 (PB-084) Poster - Expanding the use of Oncoplastic Surgery in Invasive Lobular Breast Cancer: long-term results of 476 patients treated with three different surgical approaches

Solitary gastric metastasis from invasive lobular breast cancer misdiagnosed as gastritis: a case description.

Solitary gastric metastasis from invasive lobular breast cancer misdiagnosed as gastritis: a case description.

Abstract B014: Bioinformatic and in-vitro analyses identify cAMP/PKA/CREB signaling as a major molecular alteration in invasive lobular breast cancer

Abstract Invasive lobular cancer (ILC) is the second most common subtype of breast cancers after invasive carcinoma of no special type (NST) but associated with worse outcomes. Despite the known molecular differences between ILC and NST, ILC treatment is the same as stage matched NST making the development of ILC targeted therapies an urgent need. Therefore, this study was conducted to identify novel molecular alterations in ILC that could be exploited for therapeutic purposes. Differential gene expression and Geneset Enrichment and Variation analyses were performed on RNA-seq data from three large public breast cancer databases – the Sweden Cancerome Analysis Network-Breast (SCAN-B), The Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC). Pathways enriched in overlapping differentially expressed genes from these datasets were clustered using Jaccard index to identify novel pathways related to ILC. The cAMP/PKA/CREB signaling was studied in ILC, ILC-like and NST cell lines and patient-derived organoids (POD) using Forskolin, an activator of the pathway. Clinicopathological features of patients with ILC and NST in SCAN-B were similar to prior population-based studies. There was a consistent pattern of up-regulation of cAMP/PKA/CREB related signaling in ILC compared to NST tumors in SCAN-B, TCGA and METABRIC. Treatment with forskolin resulted in a greater increase in phospho-CREB in ILC cell lines and organoids compared to NST. CRISPR deletion of CDH1 in NST cell lines did not alter response of cells to forskolin as measured by phospho-CREB. Co-immunofluorescence supported the enhanced nuclear localization and subsequent phosphorylation of CREB at Serine 133 in ILC cell lines. Forskolin treatment caused growth inhibition in ILC and NST cells, with ILC cell lines being more sensitive to forskolin-mediated growth inhibition. Collectively the data indicate that the cAMP/PKA/CREB signaling is higher in ILC than NST tumors. This was consistent across three separate cancer datasets and was validated in cell lines and organoids. Loss of CDH1 is not sufficient to mediate this phenotype in lobular tumors. Future studies should investigate the mechanisms for differential cAMP/PKA/CREB signaling in ILC and NST and investigate the potential for therapeutic targeting especially in patients with ILC. Citation Format: Abdalla Wedn, Susrutha Puthanmadhom-Narayanan, Adrian Lee, Steffi Oesterreich. Bioinformatic and in-vitro analyses identify cAMP/PKA/CREB signaling as a major molecular alteration in invasive lobular breast cancer [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 B014.

Efficacy of Single-Agent Chemotherapy in Endocrine Therapy-Refractory Metastatic Invasive Lobular Carcinoma.

Hormone receptor (HR)-positive, HER2-negative metastatic invasive lobular breast cancer (mILC) is distinct from invasive ductal cancer (IDC) in clinicopathologic and molecular characteristics, impacting its response to systemic therapy. While endocrine therapy (ET) combined with targeted therapies has shown efficacy in ET-sensitive mILC, data on chemotherapy in ET-refractory mILC remain limited. We investigated the efficacy of single-agent capecitabine (CAP) versus taxanes (TAX) in ET-refractory HR+ HER2-negative patients with mILC. Using data from the MD Anderson prospectively collected breast cancer database, we identified patients with HR+ HER2-negative mILC who received prior ET and first-time chemotherapy in the metastatic setting. We compared outcomes between 173 CAP-treated and 96 TAX-treated patients. CAP-treated patients had significantly better median progression-free survival (PFS) than TAX-treated patients (8.8 vs 5.0 months, HR 0.63, P < .001). Overall survival (OS) did not differ significantly between the groups (42.7 vs 36.6 months for CAP vs TAX, respectively, HR 0.84, P = .241). Multivariate analyses for PFS and OS revealed better outcomes in subjects with fewer metastatic sites and those exposed to more lines of ET. Additionally, Black patients showed worse OS outcomes compared to White patients (HR 2.46; P = .001). In ET-refractory HR+ HER2-negative mILC, single-agent CAP demonstrated superior PFS compared to TAX. Our findings highlight the potential benefit of CAP in this patient subset, warranting further investigation through prospective trials.

Association of Race, Ethnicity, Language, and Insurance with Time to Treatment Initiation Among Women with Breast Cancer at an Urban, Academic, Safety-Net Hospital.

Initial treatment for nonmetastatic breast cancer is resection or neoadjuvant systemic therapy, depending on tumor biology and patient factors. Delays in treatment have been shown to impact survival and quality of life. Little has been published on the performance of safety-net hospitals in delivering timely care for all patients. We conducted a retrospective study of patients with invasive ductal or lobular breast cancer, diagnosed and treated between 2009 and 2019 at an academic, safety-net hospital. Time to treatment initiation was calculated for all patients. Consistent with a recently published Committee on Cancer timeliness metric, a treatment delay was defined as time from tissue diagnosis to treatment of greater than 60 days. A total of 799 eligible women with stage 1-3 breast cancer met study criteria. Median age was 60 years, 55.7% were non-white, 35.5% were non-English-speaking, 18.9% were Hispanic, and 49.4% were Medicaid/uninsured. Median time to treatment was 41 days (IQR 27-56 days), while 81.1% of patients initiated treatment within 60 days. The frequency of treatment delays did not vary by race, ethnicity, insurance, or language. Diagnosis year was inversely associated with the occurrence of a treatment delay (OR: 0.944, 95% CI 0.893-0.997, p value: 0.039). At our institution, race, ethnicity, insurance, and language were not associated with treatment delay. Additional research is needed to determine how our safety-net hospital delivered timely care to all patients with breast cancer, as reducing delays in care may be one mechanism by which health systems can mitigate disparities in the treatment of breast cancer.

Histologic tumor type as a determinant of survival in hormone receptor-positive, HER2-negative, pT1-3 invasive ductal and lobular breast cancer

PurposeThe aim of the study was to compare the difference in survival between invasive ductal (IDC) and lobular carcinoma (ILC).MethodsData of patients (n = 1843) with a hormone receptor-positive, HER2-negative, pT1-3 IDC or ILC cancer without distant metastasis, treated at the Ghent University Hospital over the time period 2001–2015, were analyzed.ResultsILC represented 13.9% of the tumors, had a higher percentage of pT3 and pN3 stages than IDC, lymphovascular space invasion (LVSI) was less present and Ki-67 was mostly low. 73.9% of ILCs were grade 2, whereas IDC had more grade 1 and grade 3 tumors. Kaplan–Meier curves and log-rank testing showed a significant worse DFS for ILC with pN ≥ 1 than for their IDC counterpart. In a multivariable Cox regression analysis the histologic tumor type, ductal or lobular, was a determinant of DFS over 120 months (IDC as reference; hazard ratio for ILC 1.77, 95% CI 1.08–2.90) just as the ER Allred score (hazard ratio 0.84, 95% CI 0.78–0.91), LVSI (hazard ratio 1.75, 95% CI 1.12–2.74) and pN3 (hazard ratio 2.29, 95% CI 1.03–5.09). Determinants of OS over ten years were age (hazard ratio 1.05, 95% CI 1.02–1.07), LVSI (hazard ratio 3.62, 95% CI 1.92–6.82) and the ER Allred score (hazard ratio 0.80, 95% CI 0.73–0.89).ConclusionThe histologic tumor type, ductal or lobular, determines DFS in hormone receptor-positive, HER2-negative, pT1-3 breast cancer besides the ER Allred score, LVSI and pN3.

The effect of (neo)adjuvant chemotherapy on long-term survival outcomes in patients with invasive lobular breast cancer treated with endocrine therapy: A retrospective cohort study.

Despite histological and molecular differences between invasive lobular carcinoma (ILC) and invasive carcinoma of no special type, according to national treatment guidelines no distinction is made regarding the use of (neo)adjuvant chemotherapy. Studies on the long-term outcome of chemotherapy in patients with ILC are scarce and show inconclusive results. All patients with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative ILC with an indication for chemotherapy treated with adjuvant endocrine therapy were selected from the Erasmus Medical Center Breast Cancer database. Cox proportional hazards models were used to estimate the effect of chemotherapy on recurrence-free survival (RFS), breast cancer-specific survival (BCSS), and overall survival (OS). A total of 520 patients were selected, of whom 379 were treated with chemotherapy and 141 were not. Patients in the chemotherapy group were younger (51 vs. 61 years old; p<.001), had a higher T status (T3+, 33% vs. 14%; p<.001), and more often had lymph node involvement (80% vs. 49%; p<.001) in comparison to the no-chemotherapy group. After adjusting for confounders, chemotherapy treatment was not associated with better RFS (hazard ratio [HR], 1.20; 95% confidence interval [CI], 0.63-2.31), BCSS (HR, 1.24; 95% CI, 0.60-2.58), or OS (HR, 0.97; 95% CI, 0.56-1.66). This was also reflected by adjusted Cox survival curves in the chemotherapy versus no-chemotherapy group for RFS (75% vs. 79%), BCSS (80% vs. 84%), and OS (72% vs. 71%). Chemotherapy is not associated with improved RFS, BCSS, or OS for patients with ER+/HER2- ILC treated with adjuvant endocrine therapy and with an indication for chemotherapy.

THU495 Glutamate Metabolic Enzymes GLUD1/2 And GPX4 Are Associated with Tumor Size In Black Women With Invasive Lobular Breast Cancer

Abstract Disclosure: T. Young: None. T.C. Abalum: None. N. Hodgins: None. S. Persaud: None. A.I. Fernandez: None. A.O. Olukoya: None. A.M. Rozeboom: None. R.B. Riggins: None. Background and Objective: Invasive Lobular Breast Cancer (ILC) is a special histologic type of breast cancer with unique genetic and biological features. ILC may be less dependent on glucose metabolism than the more common histologic type, invasive ductal breast cancer (IDC), instead relying more on lipid and amino acid metabolism. Our lab has previously published that expression of metabotropic glutamate receptors is increased in more rapidly growing and therapy-resistant cell line models of ILC. We hypothesized that increased expression of glutamate transporters and regulatory enzymes is associated with poor prognostic features. Methods and Analysis: We used multispectral immunohistochemical staining to measure the expression of four functionally related proteins: CD98, GLUD1/2, GPX4, and SLC7A11 in a cohort of 72 women with ILC (23.5% Black, 64.7% White, 11.8% Other). The cohort was in a two-fold redundant tissue microarray (TMA) format comprised of primary tumors collected by the Georgetown University Histopathology and Tissue Shared Resource. SLC7A11 and CD98 form a heterodimer that exports glutamate from, and imports cystine to, the cell. GLUD1/2 are two isoenzymes that convert glutamate into α-ketoglutarate to replenish the TCA cycle, or recycle ammonia to support amino acid synthesis. GPX4 is an enzyme that protects cells from lipid peroxidation-induced death. We compared expression of these proteins with clinical, pathological, and demographic variables (overall survival, hormone receptor expression, tumor size, race, age) using t test/ANOVA, Kaplan-Meier survival analysis, and linear regression. Results: In the 68 evaluable cases, the percentage of ILC tumor cells stained positive for GLUD1/2 and GPX4 was significantly higher than for CD98 or SLC7A11 (P&amp;lt;0.001), so further analyses focused on these. Women with a combination of high (above median) GLUD1/2+ (&amp;gt;49%) and GPX4+ (&amp;gt;54%) expression had a trend toward decreased survival (Hazard Ratio, HR 3.53, P=0.159). GPX4, GLUD1/2, and estrogen receptor (ER) expression were associated with tumor size in the entire cohort (R2 = 0.124, P = 0.041), but this relationship was markedly stronger in Black women (R2 = 0.487, P = 0.040). In univariate analyses, GLUD1/2 (R2 = 0.43, P&amp;lt;0.01) and GPX4 (R2 = 0.27, P&amp;lt;0.05) expression were each associated with tumor size in Black women, but not in the entire cohort. GPX4 expression and tumor size were both significantly higher (P&amp;lt;0.05) in Black women over 60 years of age, compared to those under 60. Conclusion: GLUD1/2 and GPX4 expression may be prognostic in ILC, as our results show that tumor size increases with higher expression of these proteins (especially among Black women). Limitations of this study include small sample size and lack of an independent cohort for validation. Future studies will include analysis of these proteins in a TMA comprised of tissue from women with IDC. Presentation: Thursday, June 15, 2023

THU643 Hyperandrogenism Caused By A Steroid Cell Tumor Of The Ovary In A Postmenopausal Woman

Abstract Disclosure: M.S. Myint: None. A. Pinero-Pilona: None. Introduction Steroid cell tumor-not otherwise specified (SCT-NOS) is a subtype of steroid cell tumors which, in turn, is a subtype of sex cord-stroma tumors of the ovary. SCTs are exceedingly rare, account for less than 0.1% of all ovarian tumors, can secrete androstenedione, α-hydroxyprogesterone, and testosterone, and cause hyperandrogenism. We present a case of SCT-NOS, which was revealed postoperatively and was associated with breast cancer. Clinical Case A 74-year-old postmenopausal woman presented approximately a year after the onset of hirsutism, frontal alopecia and an elevated serum total testosterone (TTST) 341 ng/dl (reference range 3 to 41 ng/dL) and free testosterone (FRTST) 10.5 pg/mL (reference range 0.0 to 4.2 pg/mL). She has no clitoromegaly, acne, striae, or changes in voice and no history of infertility or PCOS. Physical examination was significant for cushingoid appearance, frontal alopecia, and hirsutism on the face. Her estradiol level was 213 pg/mL (reference range 0 to 30 pg/mL), FSH and LH levels were in the postmenopausal range, 17-hydroxyprogesterone, DHEA-sulfate, androstenedione, and morning cortisol were normal. Pelvic ultrasonography and CT of the abdomen and pelvis did not reveal an adrenal or ovarian abnormality. We suspected an ovarian source and thus recommended bilateral oophorectomy due to the markedly elevated testosterone level and postmenopausal status. We also started spironolactone. Before setting up for surgery, she was diagnosed with invasive lobular left breast cancer and underwent surgery and radiotherapy. Then, she had bilateral salpingo-oophorectomy. After surgery, TTST dropped to 4 ng/dL and FRTST to 2 pg/mL. Her hyperandrogenic symptoms significantly subsided. Pathology revealed a 1.5 cm red-brown nodule within the left ovary. The nodule contains polygonal cells with vacuolated cytoplasm arranged in nests, cords, and sheets. Cells were positive in calretinin and inhibin and negative in Reinke crystal. A steroid cell tumor, NOS was confirmed. Pathologic features associated with aggressive clinical behavior were not present. Conclusion The incidence of SCT-NOS is highest in women of childbearing age but rare in postmenopausal women. There were only a few case reports of SCT-NOS, most of which are relatively larger and revealed on imaging. In our case, the imaging did not localize the tumor. Sex cord-stromal tumors are often not visualized on imaging. Failure to identify a tumor on imaging does not rule out the presence of a tumor. One should always rule out androgen-secreting tumors in cases of significantly high testosterone. When imaging fails to reveal a tumor, bilateral oophorectomy should be considered in postmenopausal women and an ovarian and adrenal venous sampling in women of childbearing age. It is worth doing so because hyperandrogenism is associated with an increased risk of endometrial and breast cancer. Presentation: Thursday, June 15, 2023