Abstract P1-03-30: Genomic risk score distribution and outcomes of patients with early-stage breast cancer diagnosed during pregnancy

Abstract Background: Breast cancer (BC) diagnosed during pregnancy has been associated with worse prognosis, potentially due to pregnancy-associated changes in the local and systemic hormonal and immune environments, and cytokine profiles. Oncotype DX Breast Recurrence Score® test is a prognostic biomarker, predictive of chemotherapy benefit in patients (pts) with early-stage, estrogen receptor-positive (ER+), HER2-negative (HER2-) BC, though there are limited data regarding its use in pregnant women. The aim of this study was to evaluate the distribution of Recurrence Score® (RS) results and the long-term outcomes of pts with ER+, HER2- BC diagnosed during pregnancy. Methods: Women with stage I-III, ER+, HER2- BC diagnosed during pregnancy were identified from a prospective cohort study of pts newly diagnosed with BC at age ≤40 years, enrolled from 2006 to 2016. Pts were classified as pregnant or not pregnant at the time of BC diagnosis. The non-pregnant group was subdivided into nulligravid or in the postpartum period. RS were obtained from banked samples when not clinically performed. RS results were classified as low (<11), intermediate (11-25) or high (> 25) and were correlated with clinicopathological characteristics and outcomes. Descriptive analyses were summarized for pts characteristics. RS results were compared by Wilcoxon Rank Sum test. Distant recurrence-free interval (DRFI) was estimated with Kaplan-Meier methods. Results: From 403 pts with stage I-III, ER+, HER2- BC, with clinical or research-obtained RS results and available gravidity history, 16 (4.0%) were pregnant and 387 (96.0%) were not pregnant at BC diagnosis (117 [29.0%] nulligravid and 270 [67.0%] postpartum). Median follow-up was 11.1 years. Median age at diagnosis was 36 and 37 years, node positivity (N+) rate was 8 (50.0%) and 146 (37.7%), and chemotherapy was administered to 15 (93.8%) and 276 (71.3%) pregnant and non-pregnant women, respectively. Among pts diagnosed during pregnancy, 15 (93.8%) had had prior pregnancies and 5 (31.3%) were diagnosed with stage I, 7 (43.7%) with stage II, and 4 (25%) stage III BC. From those with N+ BC, 6 pts (37.5%) had N1, and 2 pts (12.5%) had N2 disease. Within the pregnant group, median RS was 30.5 (range 21-68), with 6 (37.5%) pts having an intermediate RS and 10 (62.5%) a high RS. This contrasts with non-pregnant patients whose median RS was 20 (3-77, P=0.0002). The 11-year DRFI rates for pregnant pts with node-negative BC were 100% for RS 11-25 and 75% for RS > 25; while for N+ BC, 11-year DRFI was 100% for RS 11-25 and 50% for RS > 25. Conclusion: Pts with early-stage, ER+ BC diagnosed during pregnancy had genomically intermediate- or high-risk tumors. RS results were higher among pregnant pts compared to non-pregnant women. Most pregnant pts had prior pregnancies, which may have influenced the biological characteristics of the BC diagnosed during a subsequent pregnancy. Although most pregnant patients received chemotherapy, distant relapse rates were elevated among pts with high RS. Citation Format: Guilherme Nader-Marta, Yue Zheng, Kate E. Dibble, Shoshana M. Rosenberg, Erica L. Mayer, Philip D. Poorvu, Kathryn J. Ruddy, Laura C. Collins, Jeffrey Peppercorn, Lidia Schapira, Virginia F. Borges, Christy A. Russell, Steven E. Come, Ellen Warner, Kornelia Polyak, Eric P. Winer, Ann H. Partridge. Genomic risk score distribution and outcomes of patients with early-stage breast cancer diagnosed during pregnancy [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P1-03-30.