Chondroblastic osteosarcoma in right thigh of a bitch

A 3 year-old German shepherd bitch was admitted with a severe enlargement of the right thigh. Uncapsulated large mass, 7 cm × 10 cm thickness was found at necropsy surrounding the contour of the thigh muscles along its whole length. Microscopically, the tumor composed of neoplastic cells infiltrating the stroma, with cellular pleomorphism, hyperchromatism, high atypical mitotic figures (2-4 per high power field) and focal areas of osteoid formation. Chondroblastic differentiation was also present where chondroblastic cells consisted of moderately pleomorphic, irregularly arranged polygonal cells with vacuolated cytoplasm, vesiculated nuclei and large nucleoli. Based on these pathological findings, this tumor was diagnosed as chondroblastic osteosarcoma.