Neoplasia: P01: Spontaneous mammary gland adenocarcinoma in a 37-week-old male Wistar rat

Spontaneous tumors of mammary glandare infrequent in male rats. A spontaneous adenocarcinoma of the mammary glandwas observed in a 37-week-old male WNIN (Wistar/NIN) rat from the breeding colony of IIBAT. The rat had a subcutaneous mass at the left lateral aspect of neck measuring approximately 4 cm in diameter. In our literature search, we did not find any reports of spontaneous malignant neoplasmsof the male mammary glandin this age group. The histological features of this neoplasmare similar to those described in female rats, with the exception of a lack of functional differentiation. Immunohistochemical staining of the tumor for smooth muscle actin and cytokeratin14 was positive, which is consistent with a neoplasmof mammary origin.