Damasceno, Karine Araújo. Fundação Oswaldo Cruz. Instituto Gonçalo Moniz. Salvador, BA, Brasil. “Documento produzido em parceria ou por autor vinculado à Fiocruz, mas não consta à informação”.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (470696/2011-7), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and Fundação de Amparo a Pesquisa de Minas Gerais (FAPEMIG), Brazil.Studies about canine mammary tumors based on single molecular markers probably cannot accurately account for the heterogeneity of this disease, and the investigation of multiple molecular alterations in primary tumors and their metastases, in conjunction, has assumed great importance for the understanding of mammary tumor progression. In the present study, we selected 54 primary mammary carcinomas with lymph node metastasis (T1,2,3N1M0), 29 primary mammary carcinomas without metastasis (T1,2,3N0M0), and 25 canine lymph nodes metastasis to evaluate the immunohistochemical expression of HER-2, EGFR, Cox-2 and Ki67 and its association with clinical-pathological parameters and overall survival. Our results found a concordance between the expression of HER-2 (K coefficient: 0.250), Cox-2 (K coefficient: 0.571), and Ki67 (K coefficient: 0.397) and a discordance between EGFR expression (K coefficient: -0.195) in primary mammary carcinomas and paired lymph node metastasis. Furthermore, a high Ki67 index (>24%), large tumor size and the presence of angiolymphatic invasion in canine primary mammary carcinoma with lymph node metastasis plus the presence of extracapsular extension in lymph nodes metastasis were also related to worse prognoses and shorter overall survival (P<0.05). In conclusion, our study demonstrates that primary mammary carcinomas with high expression of HER-2, Cox-2 and Ki67 also show high expression of these markers in paired lymph node metastasis. Moreover, the expression of these molecular markers in lymph nodes metastasis did not demonstrate a prognostic relevance.