Clinical outcome of parosteal osteosarcoma

BACKGROUND: Parosteal osteosarcoma is a rare type of osteosarcoma with distinct characteristics. Clinical outcome of 21 patients was analyzed to assess the predictive relevance of surgical margin, intramedullary tumor extension and histologic grade. METHODS: There were 5 mens and 16 womens with an average age of 26 years. Average follow-up was 9.1 years (range 2.5-22.1). Most common sites were distal femur (15) and proximal humerus (2). No patient presented with metastasis. Surgical margin was wide in 13 and marginal in 8. Intramedullary extension was seen in 10 patients (48%). Focal high-grade 2 and 3 tumors were seen in 11 (52%) and 3 (14%) patients respectively. RESULTS: Twenty patients (95%) were alive without disease. Two (10%) had relapse, one with local recurrence and another with local recurrence and lung metastasis. Of eight marginal procedures performed, 2 turned out to have histologically tumor-positive margins, both of whom later developed relapses. All patients with histologically negative margins remained disease-free. Presence of intramedullary extension and focal high-grade tumor was not significantly associated with relapse. CONCLUSIONS: A marginal but histologically negative margin of excision appears adequate for parosteal osteosarcoma. However, long-term follow-up is warranted for monitoring of rare incidences of local recurrences or distant metastases.