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Background: How treatment shapes survival after breast-cancer recurrence in Latin America remains poorly described. We extended follow-up of the Latin American Cancer Research Network cohort to quantify post-recurrence overall survival, describe systemic-therapy pathways, and assess the robustness of survival estimates to incomplete follow-up. Methods: We conducted a cohort study of women enrolled with stage I-III breast cancer at 31 centres in Argentina, Brazil, Chile, Mexico, and Uruguay between 2011 and 2014. Vital status and systemic treatments were updated from medical records to July 1, 2025. The main outcome was overall survival after recurrence, defined from first recurrence to death from any cause or censoring. Kaplan-Meier curves and log-rank tests compared survival by immunohistochemistry-defined subtype. Adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated with a Firth-penalised Cox model. Sensitivity analyses included best-case and worst-case censoring, inverse-probability-of-censoring weighting, and Fine-Grey competing-risk regression. Systemic-therapy sequences were reconstructed for up to six lines. Findings: Vital status was updated for 970 of 1191 women (81.4%), and 162 had a documented first recurrence. Median overall survival after recurrence was 24.0 months (IQR 9.6-45.6). Compared with triple-negative breast cancer, adjusted HRs were 0.64 (95% CI 0.20-1.77) for hormone receptor-negative/HER2-positive disease, 0.54 (0.26-1.14) for hormone receptor-positive/HER2-negative disease, and 0.93 (0.39-2.20) for hormone receptor-positive/HER2-positive disease. Chemotherapy was the first-line regimen in 83 of 162 patients (51%), endocrine monotherapy in 55 of 162 (34%), and trastuzumab-pertuzumab-taxane or cyclin-dependent kinase 4 and 6 inhibitor-based regimens in eight of 162 (5%). Overall, 87 of 162 patients (54%) initiated second-line therapy. Interpretation: Adjusted subtype HRs were imprecise and should be interpreted cautiously. Steep treatment-line attrition, limited uptake of contemporary targeted therapies, and incomplete follow-up in some health-system settings indicate modifiable regional gaps in metastatic breast-cancer care. Funding: ASCO Conquer Cancer Center for Global Health at the United States-National Cancer Institute at the National Institutes of Health (contract award No. HHSN2612010000871/NO2-PC-2010-00087); Fogarty International Center, NIH, HHS; and Susan G. Komen for the Cure; in Argentina, Instituto Nacional del Cáncer (Ministry of Health), Fundación Argentina de Nanotecnología, Agencia Nacional de Promoción Científica y Tecnológica, CONICET (Ministry of Science, Technology, and Productive Innovation); Brazil, Ministério da Saúde (Ministry of Health); Chile, Instituto de Salud Pública (Public Health Institute) and Ministerio de Salud (Ministry of Health); and Mexico, Consejo Estatal de Ciencia y Tecnología de Jalisco (COECYTJAL) and Universidad de Sonora (University of Sonora).
Retamales et al. (Fri,) studied this question.