Clinical, pathological and immunohistochemical characterization of spontaneous neoplasms in pet rodents in Northeastern Brazil

In the last decade, there has been a significant increase in the demand for small rodents such as hamsters, guinea pigs, rats, and mice to be kept as pets. Consequently, the veterinary care provided to these animals has also increased. The aim of this study was to describe gross, histopathological and immunohistochemical findings of 26 spontaneous neoplasms diagnosed in 25 pet rodents in Northeastern Brazil. A retrospective study was carried out from 2014 to 2022 in two veterinary diagnostic laboratories to identify cases of tumoriform lesions in these species. Hamsters represented the most frequent species in this study (60%, 15/25), followed by rats (28%, 7/25), guinea pigs (8%, 2/25), and mice (4%, 1/25), with a mean age of 17.63 months. The anatomical regions of the face/head and thoracic region were the most affected. The most affected tissues were the skin/subcutaneous/mucosal (65%, 15/26) and mammary gland (23%, 6/26). Eighteen different types of neoplasms were diagnosed, and T-cell lymphomas and mammary adenocarcinomas were the most diagnosed tumors, each corresponding to 12% (3/26) of the cases. Leiomyosarcoma, myxosarcoma and mammary adenocarcinoma metastases were also noted. Immunohistochemistry was essential for the diagnosis of certain malignant mesenchymal and round-cell neoplasms. Pet rodent neoplasms in Northeastern Brazil are common, especially in hamsters, and immunohistochemistry can be a useful tool for the definitive diagnosis of these tumors.