A mammary gland chondrolipoma in the dog

A 12-year-old intact female dog was submitted to surgery to remove a well-circumscribed mass located near the left inguinal mammary gland. At histological examination, the mass was unencapsulated and composed by lobules of fat cells and scattered isles of cartilaginous tissue. Chondroblasts and chondrocytes showed moderate signs of atypia and often were located singularly or in small clusters within the stroma of the neoplasm. Immunohistochemical analysis revealed that cells were vimentin and S-100 positive, whereas no immunoreactivity was showed for cytokeratin, cytokeratin 5/6, cytokeratin 14, and P63. A diagnosis of chondrolipoma was made based on microscopic findings.