Extraskeletal Osteosarcoma: Outcomes and the Role of Chemotherapy

Extraskeletal osteosarcoma (EO) is a malignant neoplasm that produces osteoid, bone, and chondroid material without direct attachment to bone or periosteum. Surgical resection is the mainstay of treatment; the role of chemotherapy is not well defined. Therefore, we evaluated the impact of chemotherapy in the survival of patients with EO.

All EO patients seen at Mayo Clinic between 1990 and 2014 were assessed. Forty-three patients were included after all archived pathology slides were reviewed to confirm the diagnosis of EO.

Of 43 patients, 37 patients had localized disease and 6 patients had metastatic disease at diagnosis. Chemotherapy was used in 73% and 75% of patients, respectively. Chemotherapy was predominantly anthracycline based, and included platinum in 22 patients (84%).Median overall survival (OS) and progression-free survival (PFS) were 50 months (95% confidence interval, 25-99), and 21 months (95% confidence interval, 13-not reached), respectively. There was a trend towards longer OS and PFS in patients who received chemotherapy. Those who received platinum-based therapy had remarkably prolonged OS (median, 182 vs. 18 mo; 5-year, 61% vs. 0%; P=0.01) and PFS (median, not reached vs. 10 mo; 5-year, 56% vs. 0%; P=0.005). Baseline characteristics were similar in the platinum and nonplatinum group.In patients who received chemotherapy, relapse/recurrence rate was lower in the platinum-based group (41%) as opposed to the nonplatinum-based group (100%; P=0.02). In the neoadjuvant setting, the overall response rate of platinum-containing regimens was 27%.

Our results suggest a clinical benefit when platinum-based chemotherapy is incorporated in the management of patients with EO. We plan to validate this further with an expanded multicenter analysis.