Osteoblastoma-like osteosarcoma. The Rizzoli Institute experience.

A series of 11 osteosarcomas that histologically resembles osteoblastoma was reviewed. The ages of the seven males and four females ranged from 19 to 47 yr (average 29). In six patients the roentgenograms showed cortical destruction and poorly defined borders on the lesion; this roentgenographic presentation was suggestive of malignancy. Histologically, the tumor permeation of the surrounding host tissue allowed us to differentiate osteoblastoma-like osteosarcoma from osteoblastoma. The differential diagnosis can be very difficult or even impossible on a small biopsy. The first diagnosis was considered benign in nine of our cases. Osteoblastoma-like osteosarcoma is a rare variety of osteosarcoma (1.1% of all osteosarcoma). It is a low-grade malignant lesion in which recurrence is the rule when adequate surgical margins were not achieved (five patients). Two of these patients died from tumors after inadequate surgical treatment of the primary tumor as well as of the recurrences. The six patients who were treated with wide surgical margins were alive without recurrence. One of them had lung metastasis, twice, treated with wide-wedge resection. Osteoblastoma-like osteosarcoma is a low-grade variety of osteosarcoma with characteristic histopathologic features. It needs to be recognized by the pathologist to achieve the right treatment which is wide surgical procedure.