Abstract PS5-04-20: Clinicopathologic Features and Outcomes of Breast Cancer in Young Women Treated at a National Oncology Institute in the Dominican Republic

Abstract Abstract Background: Breast cancer in women ≤40 years represents a minority of cases but carries a disproportionate burden due to its biological aggressiveness, psychosocial impact, and economic consequences. Young women often present with advanced disease and triple-negative or HER2+ subtypes, associated with higher recurrence rates. Evidence from Latin America and the Caribbean is scarce, and reports from the Caribbean are virtually absent. Characterizing this population is essential to guide regional cancer control strategies and improve outcomes. Methods: We conducted a retrospective cohort study of women aged 18-40 years diagnosed with breast cancer between 2015 and 2020 at the Instituto de Oncología Dr. Heriberto Pieter, the national reference center in the Dominican Republic. Demographic, clinicopathologic, and therapeutic data were collected. Survival was calculated in years and stratified by stage and subtype. Kaplan-Meier methodology was used to estimate overall and disease-free survival. Between 2015 and 2020, 3,074 breast cancer patients were diagnosed, of whom 22% (n=675) were young women. After applying criteria, 283 patients were included. Results: A total of 283 patients were analyzed (median age 35 years). Most presented with advanced disease: stage IIIA 20.6%, IIIB 27.3%, IIIC 2.8%, IIB 28.7%; 12.8% had de novo stage IV. Subtypes were HR+/HER2- 61.7%, triple-negative 16.7%, and HER2+ 21.7%. Within HR+/HER2-, most tumors were Luminal B, consistent with the higher prevalence of Luminal B vs Luminal A in young women. Thus, over one-third corresponded to aggressive subtypes (triple-negative or HER2+). Treatment included mastectomy (85%), neoadjuvant chemotherapy (80%), endocrine therapy (68%), and radiotherapy (73%). Only 50% of HER2+ patients received targeted therapy, underscoring limited access. After a mean follow-up of 5.7 years, recurrence occurred in 35% of stage I-III patients, predominantly distant. Lung was the most frequent site (43%), followed by bone (32%), liver (25%), and CNS (13%). Mean overall survival declined by stage: 7.1 years in stage II, 5 years in stage III, and only 2.5 years in stage IV. Conclusions: In this large single-institution cohort, most young women were diagnosed at advanced stages, with aggressive subtypes in more than one-third of cases. Recurrence was frequent and mainly distant, with lung and bone as leading sites. Survival was markedly reduced in advanced stages, particularly stage IV. The gap between HER2+ prevalence and limited targeted therapy reflects restricted access to modern agents, likely contributing to poor outcomes. These findings represent one of the first comprehensive reports on breast cancer in young women from the Caribbean and highlight the urgent need for early detection, equitable access, and policies tailored to this vulnerable group. Keywords breast cancer, young women, Latin America, survival, clinicopathologic features Citation Format: M. B. Rojas, Evelyn Ruiz, Cindy Jiménez, Angela Grano de Oro, Vilma Núñez, Rosa Vassallo. Clinicopathologic Features and Outcomes of Breast Cancer in Young Women Treated at a National Oncology Institute in the Dominican Republic abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-04-20.