Extraskeletal Osteosarcoma: Outcomes and the Role of Chemotherapy.

Objectives: 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.

Methods: 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.

Results: 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%.

Conclusions: 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.