Low-grade intraosseous osteosarcoma.

A study of 80 well-differentiated osteosarcomas, 16 from the Mayo Clinic files and 64 from our consultation files, revealed that males and females were about equally affected, most of the patients were young adults, and skeletal distribution was similar to the distribution seen in conventional osteosarcoma. Radiographs generally showed poor margination, suggestive of malignancy. Histologically, the tumors were composed of spindle cells with only minimal atypia. Some tumors had bone spicules similar to those seen in fibrous dysplasia. An invasive growth pattern was the most helpful feature in differentiating low-grade osteosarcoma from fibrous dysplasia. Initial treatment was highly variable. Local excision was almost always associated with recurrence. Wide excision was almost never followed by recurrence. The recurrent tumor was a high-grade, conventional osteosarcoma in 15% of the patients, and this was associated with a poor prognosis. Wide excision seems to be the treatment of choice for this very rare variant of osteosarcoma.