Mammary neoplasms have high incidence in both women and female dogs, with such a cytological resemblance between species that studies in canines might work as a baseline for research regarding the incidence in women, due to the relatively high incidence of this cancer, similar biologic behavior, large body size, comparable responses to cytotoxic agents, and shorter overall lifespan. Given the relevance of this neoplasm and the practicality of the cytological examination, studies listing the classification criteria for these tumors gains importance, aiding in diagnosis precision. Aim and Objective: Therefore, this research paper aims at identifying and standardizing criteria that may be relevant for the diagnosis of malignancy in cytopathological preparations from mammary tumors in female canines. Once the cytopathological malignancy criteria are identified, we aim at verifying whether there is variation in the tumor's degree of aggressiveness considering the criteria established for mammary cancer in women.