Cutaneous extraskeletal mesenchymal chondrosarcoma in a cat

A 4-year-old, male cat was presented with a fixed, subcutaneous mass in the lumbosacral region. Ahistopathological examination revealed a well-defined but nonencapsulated neoplasm characterized by a proliferationof predominantly spindle cells, with high mitotic activity. Interspersed between these cells were singlecellular elements with chondroid differentiation. Large areas of cartilaginous tissue with foci of endochondralossification, necrosis and myxoid tissue were also observed within the neoplastic parenchyma. A diagnosis ofextraskeletal mesenchymal chondrosarcoma was made based on the histological pattern – characterized by thecoexistence of cartilaginous islands and undifferentiated mesenchymal cells, results of Alcian blue staining atvarious pH, immunohistochemical reactivity against vimentin and S-100, and the absence of skeletal involvementor other primary tumour sites. Clinical history of the cat excluded traumas, vaccinations or other types of subcutaneousinoculation. Six months on from surgical treatment, neither recurrence nor metastases have beendetected.[...]