MAST CELL TUMOR AND MAMMARY GLAND CANCER: A CASE REPORT OF COLLISION TUMOR IN DOG

Neoplasms developing at the same venue are difficult to classify because of distinct morphological characteristics that do not fit any usual cancer classification. Collision tumors, at clinical and macroscopical examination resemble a single tumor, but histological and/or immunohistochemical analysis reveals that they are constituted by two phenotypically distinct cell populations yet maintaining sharp distinct boundaries [1]. In human medicine, collision tumors have been documented in the last decade in different anatomical sites [2]. In veterinary literature, few cases have been so far described [3,4,5,6]. A case of a collision tumor, in a 12-year-old female Labrador with a mammary gland nodular lesion, is described. Histopathological and immunohistochemical examinations revealed the presence of two distinct malignant tumors. One arose from the mammary gland epithelium, the other one was composed by neoplastic mast cells. To the authors' knowledge, this is the first description of a collision tumor in the dog composed by mast cell tumor and tubular carcinoma in the mammary gland. The raising interest for collision tumors suggests to widen their knowledge and to set up a multimodal approach including surgery and targeted therapy.