Mammary Adenoma Associated with Chronic Mastitis in a Wild Boar (Sus Scrofa)

Mammary gland tumor is rare and only a few cases have been reported in wild animals. Moreover, most etiologies of the known cases in veterinary medicine are related to age, diet, obesity, and excessive sex hormones in domestic animals while few etiologies are reported in wild animals. An unknown-aged female wild boar was presented to the Department of Veterinary Pathology, Kyungpook National University with a well-demarcated, and firm-to-elastic mammary gland mass. The cut-surface of the mass was pink-reddish, and homogeneous. Microscopically, the mass was mainly composed of well-differentiated neoplastic glandular epithelial cells characterized by a single-layer, columnar to cuboidal shapes, and small and central nuclei and nucleoli. Any evidence of invasiveness or metastases of the neoplastic cells were not observed. Interestingly, infiltration of chronic inflammatory cells such as plasma cells and macrophages was observed along with a large quantity of gram-negative and positive bacterial colonies in the mammary glands. Moreover, accompanied fibrosis of stroma was observed, as well. Based on the gross and microscopic findings, the present case was diagnosed as mammary simple adenoma caused by chronic mastitis progressing to fibrotic condition. To the authors’ knowledge, this is the first study describing the histopathological aspects of mammary gland tumors associated with chronic mastitis accompanied by fibrosis in wild animals.