Sherman, Mark E.

e12697 Background: Postpartum-associated breast cancer (PABC) has been defined clinically as breast cancer (BC) diagnosed within the first 5 years of the most recent birth. Though generally rare, incidence rates are increasing in conjunction with delayed childbearing and older maternal age at first birth. Currently, there are limited data regarding serial patient-reported outcomes in this patient population compared to non-PABC patients. Methods: Patients with PABC from the Mayo Clinic Breast Disease Registry who completed baseline, 2, and 4-year surveys were matched 1:1 to BC patients whose cancers occurred more than 5 years after their most recent birth (or in the setting of nulliparity) based on age, clinical stage, treatment received, and tumor subtype. Survey results from the Patient Health Questionnaire-2 (PHQ-2), Patient-Reported Outcomes Measurement Information System-10 (PROMIS-10), and Impact of Event Scale-Revised (IES-R) collected at approximately two and four years after diagnosis were compared between PABC and non-PABC patients. Univariable analyses used Wilcoxon rank sum tests, whereas multivariable analyses employed linear regression models adjusting for potential confounding effects. Results: A total of 222 individuals were included (111 with PABC). A higher proportion of individuals in the PABC cohort were married compared to the non-PABC cohort (80% vs. 42%, p < 0.001); otherwise, the groups were well-balanced across multiple categories, including age, gender, race/ethnicity, menopausal status, and germline mutation status. In univariable analyses, the Year 2 composite PHQ-2 score was significantly worse among individuals with non-PABC (p = 0.04), and the non-PABC cohort reported greater difficulty with sleep (p = 0.03) as measured by IES-R at Year 4. Both associations attenuated in a multivariable analysis controlling for marital status. In marital status-adjusted analyses of Year 4 survey results, PABC participants reported greater difficulty in carrying out social activities but were less likely to report emotional distress as evaluated by PROMIS-10 (compared with non-PABC participants). No other variables were significant univariably or multivariably (p > 0.05). Conclusions: In general, quality of life is similar among survivors of PABC compared to those diagnosed with breast cancer outside the postpartum period (or when nulliparous). However, our findings reveal that individuals with PABC are less likely to experience emotional distress 2 and 4 years after the BC diagnosis, which is unexpected, given that postpartum patients typically report higher levels of distress compared to their non-postpartum counterparts. Further investigation into these findings is warranted.

Abstract Background The incidence of early onset breast cancers (BCs) has increased, paralleling rising trends in delayed childbearing. We hypothesize that a distinct postpartum BC (PPBC) subtype, identifiable by time since last birth (TSLB) and biomarker expression, contributes to this trend. Methods We applied GeoMx Digital Spatial Profiling (DSP) to measure associations between TSLB and 71 proteins in 640 BCs from women aged ≤40 years included in the Young Women’s Breast Cancer Study. We analyzed data using univariable linear regression and multivariable sliced inverse regression to account for higher order interactions among biomarkers. Results In keratin-rich segments, progesterone receptor (PR) (P = 1.00 × 10−4) and PTEN (P = 1.00 × 10−3) were associated with longer TSLB; multivariable analyses revealed positive associations for GZMB (P = 4.00 × 10−4), SMA (P = 1.00 × 10−4), and NF-1 (P = 1.00 × 10−3). In keratin-poor segments, univariable significant positive associations were found for PR (P = 2.00 × 10−4) and PTEN (P = 1.00 × 10−3), whereas CD20 (P = 3.00 × 10−4) and CTLA4 (P = 4.00 × 10−5) were negatively associated; multivariable significant associations were found for fibronectin (P = 3.00 × 10−5) and pan-Akt (P = 1.00 × 10−3). Associations persisted after adjustment for multiple comparisons and BC molecular subtypes. Associations including for PR, PTEN, and CD20 were strongest among women with the shortest TSLB. OPAL multiplex immunofluorescence assays for PR, PTEN, CD20, SMA, and CTLA4 replicated several DSP findings, particularly when stratified by subtype and with compartment matching. In TCGA, RNA species linked to proteins associated with TSLB correlated strongly with a T-cell exhaustion signature previously linked to poor prognosis among premenopausal women. Conclusion These data support PPBC as a biologically coherent phenotype defined by TSLB and biomarker profile, with potential implications for prevention and therapy.

Abstract Background: Postpartum breast cancer (PPBC) is associated with increased morbidity and mortality among women within 5 to 10 years following childbirth. The postpartum breast undergoes involution, involving tissue remodeling and immune cell infiltration, potentially creating a pro-tumorigenic microenvironment. The molecular mechanisms underlying this elevated risk remain poorly understood. In this study, we compared normal breast tissue samples and human mammary epithelial cells (HMECs) from postpartum women to those from age- and BMI-matched nulliparous women to elucidate potential molecular contributors to PPBC risk. Methods: Transcriptomic profiling was performed on RNA extracted from FFPE normal breast tissues using the NanoString IO 360 and BC 360 platforms to examine gene expression in nulliparous and postpartum women under 45 years of age. HMECs were isolated from organoids derived from breast tissue samples and used for next-generation sequencing and knockdown experiments targeting STAT1 and GBP1. Gene set enrichment analysis (GSEA) was applied to NanoString and RNA-seq datasets to identify differentially enriched genes between postpartum and nulliparous women. Results: Transcriptomic analysis revealed significant upregulation of interferon-stimulated genes, including STAT1 and GBP1, in postpartum breast tissues, consistent with increased immune responses during involution. NanoString data showed that markers of cell proliferation, such as Ki67, STAT1, and GBP1, were significantly higher in samples from parous compared to nulliparous women (p &lt; 0.05). GSEA revealed that cell cycle-promoting genes (GBP1, cyclins, CDKs) were upregulated, while cyclin-dependent kinase inhibitors (CDKNs) were downregulated in postpartum breast tissues. Immunohistochemistry confirmed significantly higher expression of Ki67, STAT1, and GBP1 in postpartum versus nulliparous breast tissues (p &lt; 0.0001). Silencing STAT1 and GBP1 in HMECs resulted in decreased cell proliferation, G1 cell cycle arrest, and increased expression of CDKN1A and CDKN1C. Conclusion: These findings suggest that STAT1 and GBP1 promote proliferation in postpartum breast epithelial cells by downregulating cyclin-dependent kinase inhibitors, potentially contributing to the increased risk of PPBC. Targeting these pathways may offer novel strategies for mitigating postpartum breast cancer risk. Citation Format: Joshua Ogony, Melody Stallings-Mann, Sarah McLaughlin, Mark Sherman, Derek C. Radisky. STAT1 and GBP1 promote proliferation in postpartum breast epithelium by downregulating cyclin-dependent kinase inhibitors: implications for increased postpartum breast cancer risk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 187.

Abstract Introduction: Pseudoangiomatous stromal hyperplasia (PASH) is a benign breast lesion characterized by stromal myofibroblast accumulation. While most women with PASH do not develop breast cancer, a subset eventually does, often in the same breast where PASH was originally diagnosed, even after surgical removal of the lesion. This pattern suggests the presence of a field effect, where alterations in the PASH microenvironment extend beyond the lesion itself, potentially influencing neighboring breast tissue. This study aims to identify specific fibroblasts within PASH-containing tissues that may create a microenvironment conducive to cancer initiation. Methods: We conducted a retrospective analysis of formalin-fixed, paraffin-embedded breast tissue samples from women diagnosed with PASH, comparing those who later developed breast cancer (cases) to those who remained cancer-free (controls). Using transcriptional profiling with NanoString IO360/BC360 panels, multiplex immunofluorescence (MxIF), and spatial transcriptomics via NanoString CosMX SMI, we investigated molecular and histopathological differences. We focused on the expression of fibroblast activation markers (ITGB1, PDGFRβ) and their spatial relationships with proliferating epithelial cells, as well as changes in extracellular matrix (ECM) composition and stiffness. Results: Transcriptional profiling revealed significant upregulation of proliferation-associated genes in epithelial cells from cases. MxIF showed higher Ki-67 levels in epithelial cells from cases, with proliferating cells forming clustered regions. Activated fibroblasts expressing ITGB1 and PDGFRβ were markedly increased in cases and were located closer to proliferating epithelial cells. Spatial transcriptomics uncovered gene expression changes in fibroblasts indicative of an activated phenotype, and in epithelial cells, consistent with responses to increased tissue stiffness and mechanotransduction signaling. Polarized light imaging with picrosirius red staining revealed enhanced collagen cross-linking and thick fibril formation in cases, indicating greater ECM stiffness. Conclusions: Our findings suggest that a subset of activated fibroblasts in benign breast tissue creates a pro-tumorigenic microenvironment through ECM remodeling and increased tissue stiffness, promoting epithelial proliferation and potentially driving cancer development. The spatial proximity of these fibroblasts to proliferating epithelial cells underscores their possible role in early carcinogenesis. This study introduces the novel concept of cancer-predisposing fibroblasts in benign breast tissue, providing new insights into microenvironmental changes that precede cancer and offering potential targets for early detection and intervention. Citation Format: Nicole Cruz-Reyes, Pria Westerman, Matilde Rossi, Camila Pacheco Erak, Melody Stallings Mann, Bryan McCauley, Robert Vierkant, Stacey Winham, Mark Sherman, Amy Degnim, Derek Radisky. Activated fibroblasts in benign breast tissue are associated with subsequent breast cancer development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2083.

Abstract Introduction: Fibroadenoma is the most common type of benign breast lesion and is not traditionally considered an indicator of increased breast cancer risk. This study aimed to identify biomarkers within fibroadenoma associated with subsequent breast cancer development using patient samples from the Mayo Clinic Benign Breast Disease (BBD) cohort. Methods: We analyzed formalin-fixed paraffin-embedded (FFPE) breast biopsy samples from patients diagnosed with non-proliferative fibroadenoma who either developed breast cancer later (n=10) or remained cancer-free (n=5). NanoString RNA profiling identified differentially expressed genes in fibroblasts associated with subsequent cancer development. Immunohistochemistry was first done to compare overall expression of PI16 in this cohort. Opal multiplex immunofluorescence staining (mIF) was then performed to evaluate the expression of PI16 in fibroblasts (Vim+PanCK-) and assess immune cell infiltration (CD45+) in different tissue compartments. Fibroblasts were identified by vimentin positivity (Vim+), and epithelial cells were marked by pan-cytokeratin positivity (PanCK+). Results: Compared to patients who remained cancer-free, those who developed breast cancer showed significantly increased expression of PI16 in fibroblasts (PI16+Vim+PanCK-, 3.25-fold increase, p=0.0011). Additionally, the number of immune cells (CD45+) was significantly decreased (0.52-fold, p=0.03) in the fibroadenoma lesions of patients who later developed cancer. Conclusions: Our findings suggest that elevated expression of PI16 in fibroblasts within fibroadenoma may serve as potential biomarkers for predicting breast cancer risk for women with fibroadenoma. PI16 encodes Peptidase Inhibitor 16, which is implicated in modulating fibroblast activity and extracellular matrix remodeling—processes that can contribute to a tumor-supportive microenvironment. Elevated levels of this protein in fibroblasts suggest an altered microenvironment that may foster tumor initiation and progression. The decreased immune cell infiltration further implies an immunosuppressive microenvironment that may facilitate cancer progression. As these markers can be detected in FFPE samples, our results could lead to the development of a readily applicable clinical test to identify fibroadenoma patients at increased risk for breast cancer, enabling earlier intervention and surveillance. Citation Format: Pria Westerman, Nicole Cruz-Reyes, Camila Pacheco Erak, Robert Vierkant, Bryan McCauley, Stacey Winham, Mark Sherman, Amy Degnim, Derek Radisky. Elevated PI16 expression in fibroadenoma fibroblasts is associated with subsequent breast cancer development. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2077.

Abstract Over one million biopsies are performed annually in the U.S. to evaluate suspicious breast lesions. Most biopsies lead to a diagnosis of benign breast disease (BBD) and these women have a 1.5- to fourfold increase in subsequent breast cancer (BC) risk compared with the general population. A polygenic risk score (PRS) including 313 common variants was developed to predict BC risk in the general population and has improved performance when added to existing BC prediction models. However, the value of PRS in risk prediction models among women with BBD has not been evaluated. To evaluate the role of the established PRS, BBD, and BC risk, we pooled data from 15,194 white women (6,706 BC cases and 8,488 controls) participating in five Breast Cancer Association Consortium case-control studies. BC risk associations were evaluated by self-reported BBD history and combinations of PRS expressed in tertiles using odds ratios (OR), considering the lowest category of PRS among women without BBD as the referent. Associations were also assessed in an independent case-cohort study (831 BC cases and 1,845 controls) using hazard ratios (HR). Among the case-control studies, the PRS was strongly associated with BC risk (OR=2.50 per standard deviation increase), and associations were similar in women with (OR=2.60) and without a history of BBD (OR=2.44, p-interaction=0.23). Women with BBD have a higher risk of BC than those without BBD within each level of PRS. Compared to women without BBD and in the lowest PRS category, those with BBD and PRS in the highest tertile had 5-fold increased odds of BC (OR = 5.38; 95% CI 4.73-6.13). Associations were similar in an independent case-cohort study. These findings indicate that BBD history and PRS are independent contributors to BC risk, and consideration of both simultaneously could improve breast cancer risk prediction. Future studies are needed to integrate PRS with other risk measures to refine absolute BC risk prediction among BBD patients. Associations of BC risk with combinations of PRS (tertiles) and history of BBD in five case-control studies and a case-cohort study from the Breast Cancer Association Consortium. Case-control studies Case-cohort study PRS score range History of BBD n BC cases n controls OR (95% CI)1 n BC cases n controls HR (95% CI)2 Tertile 1 (≤ -0.57) No 1009 2692 1.00 (Ref) 117 584 1.00 (Ref) Yes 508 902 1.54 (1.35-1.76) 69 163 2.05 (1.45-2.89) Tertile 2 (-0.58, -0.03) No 1469 2001 1.97 (1.78-2.17) 181 475 1.93 (1.48-2.51) Yes 760 798 2.65 (2.34-3.01) 108 170 2.99 (2.18-4.09) Tertile 3 (≥ -0.02) No 1910 1551 3.32 (3.01-3.67) 214 336 3.28 (2.52-4.26) Yes 1050 544 5.38 (4.73-6.13) 142 117 4.83 4.25-8.02) 1.Logistic regression analysis, adjusted for study site/genomic platform and age at enrollment. OR, odds ratio; CI, confidence interval.2.Cox proportional hazards regression analysis, accounting for the case-cohort study design and adjusted for age at enrollment. HR, hazard ratio; CI, confidence interval. Citation Format: Stacey J. Winham, Mark Sherman, Robert Vierkant, Bryan McCauley, Christopher Scott, Mia Gaudet, Melissa Troester, Sandhya Pruthi, Derek Radisky, Amy Degnim, Kristan Aronson, Rachel Murphy, Pascal Guenel, Therese Truong, Jenny Chang-Claude, Heiko Becher, Montserrat Garcia-Closas, Stephen Chanock, Thomas Ahearn, Xiaohong Yang, Doug Easton, Manjeet Bolla, Celine Vachon, Breast Cancer Association Consortium. Association of polygenic risk scores with breast cancer risk among women with benign breast disease. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5241.

Abstract Reduced age-related terminal duct lobular unit (TDLU) involution has been linked to increased breast cancer risk and triple-negative breast cancer. Associations of TDLU involution levels with race and ethnicity remain incompletely explored. Herein, we examined the association between genetic ancestry and TDLU involution in normal breast tissue donated by 2014 healthy women in the United States. Women of African ancestry were more likely than European women to have increased TDLU counts (odds ratio [OR]trend = 1.36, 95% confidence interval [CI] = 1.07 to 1.74), acini counts per TDLU (OR = 1.47, 95% CI = 1.06 to 2.03), and median TDLU span (ORtrend = 1.44, 95% CI = 1.08 to 1.91), indicating lower involution, whereas East Asian descendants were associated with decreased TDLU counts (ORtrend = 0.52, 95% CI = 0.35 to 0.78) after controlling for potential confounders. These associations are consistent with the racial variations in incidence rates of triple-negative breast cancer in the United States and suggest opportunities for future work examining whether TDLU involution may mediate the racial differences in subtype-specific breast cancer risk.

Abstract Background In the United States, cancer disproportionately impacts Black and African American individuals. Identifying genetic factors underlying cancer disparities has been an important research focus and requires data that are equitable in both quantity and quality across racial groups. It is widely recognized that DNA databases quantitatively underrepresent minorities. However, the differences in data quality between racial groups have not been well studied. Methods We compared the qualities of germline and tumor exomes between ancestrally African and European patients in The Cancer Genome Atlas of 7 cancers with at least 50 self-reported Black patients in the context of sequencing depth, tumor purity, and qualities of germline variants and somatic mutations. Results Germline and tumor exomes from ancestrally African patients were sequenced at statistically significantly lower depth in 6 out of the 7 cancers. For 3 cancers, most ancestrally European exomes were sequenced in early sample batches at higher depth, whereas ancestrally African exomes were concentrated in later batches and sequenced at much lower depth. For the other 3 cancers, the reasons of lower sequencing coverage of ancestrally African exomes remain unknown. Furthermore, even when the sequencing depths were comparable, African exomes had disproportionally higher percentages of positions with insufficient coverage, likely because of the known European bias in the human reference genome that impacted exome capture kit design. Conclusions Overall and positional lower sequencing depths of ancestrally African exomes in The Cancer Genome Atlas led to underdetection and lower quality of variants, highlighting the need to consider epidemiological factors for future genomics studies.