Epidemiological, clinical, and histopathological aspects of mammary neoplasms in dogs from Rio Branco, Acre, Brazil

Mammary neoplasms are very common in the clinical routine of small animals and have an enormous histological diversity and complexity. Most of these neoplasms are classified as malignant and originate from metastases, considered the main cause of death. This study aimed to present and correlate epidemiological data with the malignancy of histological types of mammary neoplasms in dogs in the municipality of Rio Branco, Acre, Brazil. The analyzed samples were collected in collaborating hospitals and veterinary clinics, the data acquired through a questionnaire filled in by them, the clinical staging carried out through the TNM system, and the histological classification according to the Consensus regarding the Diagnosis, Prognosis, and Treatment of Canine and Feline Mammary Tumors. The fixed material was evaluated macroscopically and then subjected to classical histological processing. Histological preparations were observed under optical microscopy. The data were organized statistically using Pearson's chi-square test (p<0.05). Of the 71 samples obtained from dogs, 50 consisted of mammary neoplasms, 18 skin neoplasms, and three non-tumor lesions. Eleven breeds of dogs were identified. Among them, 48 were females and two males with an average age of 10 years and most patients intact (90%) and the minority used progestogens (16%). Of the mammary neoplasms, 94% had a malignant profile, with carcinoma in a mixed tumor being the most frequent (60%). Statistically, no correlation was observed between breed, sex, age, reproductive status, use of progestogens, mammary location, or tumor size with malignancy. In general, dogs can be affected by malignant mammary neoplasms, regardless of the mentioned variables, reinforcing the importance of clinical staging and early diagnosis for the best prognosis within the small animal clinic.