Abstract PS3-10-22: An Online Tool to Assist Decisions on Chemotherapy for Men with Luminal Early Breast Cancer

Abstract Background: Due to the rarity of male breast cancer (MBC), prognosis prediction and chemotherapy indication remain understudied. We aimed to develop a generalized model to predict outcomes and identify candidates for chemotherapy omission in luminal early-stage MBC. Methods: Luminal MBC patients from the Surveillance, Epidemiology, and End Results (SEER) program (2010-2018, N=2996) and a Chinese cohort (2000-2020, N=599) were included. SEER-derived patients (2010-2016) were split into training (N=1356) and test (N=905) sets in a 6:4 ratio; others formed the US validation set (2017-2018, N=735). Chinese patients constituted the CHN validation set. The primary outcome was overall survival (OS). Four machine learning models and a Cox-based nomogram were evaluated. Risk stratification (low-, intermediate-, and high-risk groups) was based on the tertiles of 5-year risk scores in the training set predicted by the optimal model. Survival analysis employed Kaplan-Meier, log-rank tests, and Cox regression. Results: The optimal model showed robust performance (C-indices: training set=0.715, test set=0.713, US validation set=0.742, CHN validation set=0.748). OS of three risk groups differed significantly across all datasets (all P<0.001). Chemotherapy conferred no OS benefit in low-risk patients [Univariate: training set, hazard ratio (HR)=1.87, 95% confidence interval (CI), 1.24 to 2.80, P=0.002; other sets, P=0.176, P=0.147, P=0.864, respectively. Multivariate: training set, HR=1.80, 95% CI, 1.04 to 3.10, P=0.035; test set, P=0.211; US validation set, HR=3.24, 95% CI, 0.98 to 10.73, P=0.054; CHN validation set, P=0.449]. This tool has been deployed online for free access. Conclusions: Our model accurately predicts 5-year OS rates of American and Chinese male patients with luminal early breast cancer. Its risk stratification may aid in identifying low-risk patients who may be safe to omit chemotherapy. Citation Format: Y. Gao, M. Zhang, J. Nie, G. Ye, G. Sun, L. Ma, Z. Jiang, Y. Lin. An Online Tool to Assist Decisions on Chemotherapy for Men with Luminal Early Breast Cancer [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 PS3-10-22.