Purposes: Most molecular-based published studies on breast cancer do not adequately represent the unique and diverse genetic admixture of the Latin American population. Searching for similarities and differences in molecular pathways associated with these tumors and evaluating its impact on prognosis may help to select better therapeutic approaches. Patients and Methods: We collected clinical, pathological, and transcriptomic data of a multi-country Latin American cohort of 1,071 stage II-III breast cancer patients of the Molecular Profile of Breast Cancer Study (MPBCS) cohort. The 5-year prognostic ability of intrinsic (transcriptomic-based) PAM50 and immunohistochemical classifications, both at the cancer-specific (OSC) and disease-free survival (DFS) stages, was compared. Pathway analyses (GSEA, GSVA and MetaCore) were performed to explore differences among intrinsic subtypes. Results: PAM50 classification of the MPBCS cohort defined 42·6% of tumors as LumA, 21·3% as LumB, 13·3% as HER2E and 16·6% as Basal. Both OSC and DFS for LumA tumors were significantly better than for other subtypes, while Basal tumors had the worst prognosis. While the prognostic power of traditional subtypes calculated with hormone receptors (HR), HER2 and Ki67 determinations showed an acceptable performance, PAM50-derived risk of recurrence best discriminated low, intermediate and high-risk groups. Transcriptomic pathway analysis showed high proliferation (i.e. cell cycle control and DNA damage repair) associated with LumB, HER2E and Basal tumors, and a strong dependency on the estrogen pathway for LumA. Terms related to both innate and adaptive immune responses were seen predominantly upregulated in Basal tumors, and, to a lesser extent, in HER2E, with respect to LumA and B tumors. Conclusions: This is the first study that assesses molecular features at the transcriptomic level in a multicountry Latin American breast cancer patient cohort. Hormone-related and proliferation pathways that predominate in PAM50 and other breast cancer molecular classifications are also the main tumor-driving mechanisms in this cohort and have prognostic power. The immune-related features seen in the most aggressive subtypes may pave the way for therapeutic approaches not yet disseminated in Latin America. Clinical Trial Registration: ClinicalTrials.gov (Identifier: NCT02326857).Fil: Llera, Andrea Sabina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Abdelhay, Eliana Saul Furquim Werneck. Instituto Nacional de Cancer; BrasilFil: Artagaveytia, Nora. Universidad de la Republica; UruguayFil: Daneri Navarro, Adrián. Universidad de Guadalajara; MéxicoFil: Müller, Bettina. Instituto Nacional del Cáncer; ChileFil: Velazquez, Carlos. Universidad de Sonora; MéxicoFil: Alcoba, Elsa B.. Hospital Maria Curie; ArgentinaFil: Alonso, Isabel. Centro Hospitalario Pereira Rossell; UruguayFil: Alves Da Quinta, Daniela Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina. Universidad Argentina de la Empresa; ArgentinaFil: Binato, Renata. Instituto Nacional de Cancer; BrasilFil: Bravo, Alicia Inés. Hospital Regional de Agudos
Eva Perón; ArgentinaFil: Camejo, Natalia. Universidad de la Republica; UruguayFil: Carraro, Dirce Maria. Centro Internacional de Pesquisa; BrasilFil: Castro, Mónica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Castro Cervantes, Juan M.. Umae Hospital de Especialidades Centro Medico Nacional Siglo XXI; MéxicoFil: Cataldi, Sandra. Instituto Nacional del Cáncer; UruguayFil: Cayota, Alfonso. Instituto Pasteur de Montevideo; UruguayFil: Cerda, Mauricio. Universidad de Chile; ChileFil: Colombo, Alicia. Universidad de Chile; ChileFil: Crocamo, Susanne. National Cancer Institute; Estados UnidosFil: Del Toro Arreola, Alicia. Universidad de Guadalajara; MéxicoFil: Delgadillo Cisterna, Raúl. Umae Hospital de Especialidades Centro Medico Nacional Siglo Xxi; MéxicoFil: Delgado, Lucía. Universidad de la Republica; UruguayFil: Fernandez, Elmer Andres. Area de Cs. Agrarias, Ingeniería, Cs. Biológicas y de la Salud de la Universidad Catollica de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Fejerman, Laura. University of California at Davis; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Trinchero, Alejandra. Hospital Regional de Agudos Eva Perón; ArgentinaFil: Valenzuela, Olivia. Universidad de Sonora; MéxicoFil: Vedham, Vidya. National Cancer Institute; Estados UnidosFil: Zagame, Livia. Instituto Jalisciense de Cancerología; MéxicoFil: Podhajcer, Osvaldo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin
