Introduction: A subgroup of breast carcinomas overexpress epidermal growth factor-2 (HER2). The determination of this overexpression is carried out by immunohistochemistry. The difficulty of diagnosis by this method arises when the result is ambiguous (2+), thus it is necessary to perform in situ hybridization (ISH) to determine the amplification of the HER2/neu gene. Objective: To determine if, in HER2 2+ cases, the amplification of the HER 2 / neu gene is associated with prognostic clinicopathological factors. Design: Observational, cross-sectional, descriptive study. Institution: Surgical pathology service, Guillermo Almenara Irigoyen Hospital. Lima, Peru. Participants: Cases of breast cancer HER2 2+. Methodology: We studied 117 cases of Her2 2+ breast cancer diagnosed between the years 2010 - 2015, to which ISH was subsequently performed. All the data were analyzed with the statistic...