Abstract PS3-10-16: Clinical and Histopathological Prognostic Factors and Long-Term Outcomes in Early Stage Luminal Breast Cancer: A Real-World Cohort from Brazil

Abstract The rising incidence of early-stage breast cancer has prompted critical discussion regarding the true benefit of adjuvant chemotherapy (ACT) in luminal tumors, a subtype characterized by favorable prognosis and high sensitivity to endocrine therapy (ET). While multigene assays have become increasingly central to therapeutic decision-making, their limited availability in developing countries—including within private healthcare systems—represents a significant barrier. In many cases, patients must cover the high cost of testing themselves. This highlights the pressing need to identify reliable and accessible clinicopathological markers to guide ACT decisions in resource-constrained settings. We conducted a retrospective observational study using electronic medical records from a referral cancer center in Brazil. Eligible patients were women with ER-positive, HER2-negative, clinical stage I (T1N0M0) breast cancer treated between 2016 and 2024. Patients received either ET alone or in combination with ACT. Event-free survival (EFS)—defined as time from diagnosis to recurrence or death—was evaluated using Kaplan-Meier analysis and compared using the log-rank test. Variables with p-values