Mammary tumors (MT) are the 3rd most common neoplasm in cats. The incidence rate is significantly influenced by gender, age, breed, ovarian status, and the use of progestin-based contraceptives. MTs are a group of neoplasms that is heterogeneous in terms of tissue belonging, histological structure, and biological behavior. Malignant tumors are most frequent and compile from 80% to 96% of all tumors and tumor-like mammary lesions. Mammary cancer (MC) prevails, accounting for 91.4% of all cases of malignant tumors. Invasive breast cancer is much more common than carcinoma in situ. Among histological types of breast cancer, cribriform, solid, and tubulopapillary carcinomas predominate; mucous, tubular, and papillary carcinomas are less common.