Chondromyxoid fibroma-like osteosarcoma: a distinct variant of low-grade osteosarcoma.

Chondromyxoid fibroma-like osteosarcoma is a recently described, extremely rare subtype of low-grade osteosarcoma. Two such cases were encountered among 102 cases of osteosarcoma seen in the Prince of Wales Hospital, Hong Kong, between 1984 and 1994. The first patient, a 39-year-old woman, presented with a mass in her right maxilla which was resected and mistaken as a myxoma. The tumour recurred locally four years later and she now has extensive local recurrent disease six years after initial presentation and is amenable to support treatment only. The second patient, a 28-year-old man, had a pelvic tumour which recurred in the form of a polypoid left atrial tumour and pulmonary nodules six years after operation. The left atrial tumour recurred one year after operation, and led to sudden death of the patient seven years after initial presentation. Radiologically, the tumours in both cases appeared as expansile osteolytic lesions with erosion of adjacent bone and infiltration into soft tissue. Histologically, they consisted of lobules of spindle, stellate or polygonal tumour cells showing mitotic activity and with moderate nuclear pleomorphism and hyperchromatism, set in a highly myxoid stroma superficially mimicking chondromyxoid fibroma. The histological hallmark was the direct production of osteoid by tumour cells. Chondromyxoid fibroma-like osteosarcoma merits recognition as a distinct variant of low-grade osteosarcoma for which early appropriate surgery is indicated.