Background. Osteosarcoma is the most common type of primary malignant bone tumor in the extremities. The main purpose of this study was to determine clinical features, prognostic factors, and treatment results of patients with osteosarcoma at our center.

Methods. We retrospectively analyzed the medical records of children with osteosarcoma between the years 1994-2020.

Results. 79 patients were identified (54.4% male, 45.6% female). The most common primary site was the femur (62%). Twenty-six of them (32.9%) had lung metastasis at diagnosis. The patients were treated between 1995- 2013 according to the Mayo Pilot II Study protocol, while the others were treated with the EURAMOS protocol between the years 2013-2020. Sixty-nine patients underwent limb salvage surgery as a local treatment, whereas seven underwent amputation. The median follow-up time was 53 months (2.5-265 months). The event-free survival (EFS) and overall survival (OS) rates at 5 years were 52.1% and 61.5%. The 5-year EFS and OS rates were 69.4% and 80% in females; 37.1% and 45.5% in males (p=0.008/p=0.001). The 5-year EFS and OS rates of the patients without metastasis were 63.2% and 66.3%; with metastasis 28.8% and 51.8% (p=0.002/p=0.05). For good-responders, the 5-year EFS and OS rates were 80.2% and 89.1%; while for poor-responders, 35% and 46.7% (p=0.001). Mifamurtide was used in addition to chemotherapy as of the year 2016 (n=16). The 5-year EFS and OS rates were 78.8% and 91.7%, respectively for the mifamurtide group; 55.1% and 45.9%, respectively for the non-mifamurtide group (p=0.015, p=0.027).

Conclusions. Metastasis at diagnosis and poor response to preoperative chemotherapy were the most important predictors of survival. Females had a better outcome than males. In our study group, the mifamurtide group`s survival rates were significantly higher. Further large studies are needed to validate the efficacy of mifamurtide.

Keywords: chemotherapy, childhood, osteosarcoma, surgery, treatment