PS5-11-08: Characterization and survival outcomes of young women with breast cancer in Mexico: 5-year results of the Joven & Fuerte prospective cohort

Abstract Background: Young women with breast cancer (YWBC) comprise up to 15% of all breast cancer (BC) cases in Mexico. Joven & Fuerte, established in 2014, was the first 5-year prospective cohort of YWBC in Latin America. This study describes the clinicopathologic characteristics, treatment regimens, and survival outcomes of the complete cohort. Methods: Females aged ≤40 with recently-diagnosed BC (<3 months) were consecutively recruited at 1 private and 2 public referral centers in Mexico. Demographic data were collected from patient surveys; and clinicopathologic, treatment, and survival data from medical files. 5-year overall survival (OS), distant recurrence-free survival (DRFS), and invasive disease-free survival (IDFS) were estimated using the Kaplan-Meier method, specifying date of diagnosis as the time origin. Survival differences between groups were assessed with the log-rank test and Cox proportional hazard model. Results: 588 patients were included. Their median age at diagnosis was 36 years (IQR 32-38) and most had public healthcare (79%). Clinical stage distribution was: 0 (2%), I (9%), II (43%), III (35%), and IV (11%). The most frequent subtype was Luminal B (31%), followed by triple negative (TNBC) (26%), HER2 positive (22%), and Luminal A (17%). Among 513 (87%) patients with stage I-III BC, surgical management included mastectomy in 69% vs breast-conserving surgery in 22%, and axillary dissection in 56% vs sentinel lymph node biopsy in 35%. Overall, 84% received chemotherapy, 68% radiotherapy, 58% endocrine therapy, and 19% anti-HER2 therapy. Of 324 (55%) patients with stage II-III HER2 positive or TNBC, or stage II hormone-sensitive BC, 233 (72%) received neoadjuvant chemotherapy. Of these, 40% had pathological complete response (pCR). After a median follow-up of 5 years, the full cohort did not reach median survival times for any endpoint. Only patients with stage IV BC reached a median OS of 55 months (95%CI 26-not reached). Stage III was associated with worse OS, DRFS, and IDFS (all p<.001), and TNBC with worse OS (p=0.003) and DRFS (p=0.038). Very young patients (≤30 years) also exhibited worse DRFS (p=0.007) and IDFS (p=0.025). In Cox multiple regression (Table), significant associations remained between stage III and worse OS, DRFS, and IDFS, between TNBC and worse OS and DRFS, as well as between age ≤30 and worse DRFS and IDFS. Conclusions: In this cohort of YWBC, 5-year survival outcomes were significantly worse among patients with advanced stage, TNBC, and ≤30 years at diagnosis. These findings underscore the importance of BC downstaging and increased access to treatment options particularly for patients with TNBC, who could experience improved prognosis with complete treatment regimens. Moreover, this study suggests that patients aged ≤30 might comprise a specific subgroup of extremely young patients who face worse outcomes than YWBC aged ≤40. Citation Format: F. Mesa-Chavez, A. Platas, E. A. Lopez-Martinez, B. F. Vaca-Cartagena, A. S. Ferrigno, A. Fonseca, M. Miaja, M. Cruz-Ramos, J. E. Bargallo-Rocha, P. Cabrera-Galeana, A. Mohar, C. Villarreal-Garza. Characterization and survival outcomes of young women with breast cancer in Mexico: 5-year results of the Joven & Fuerte prospective cohort [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 PS5-11-08.