Background: The occurrence of osteosarcoma in elderly patients has recently been increasing, and the outcome is poor. This multi-institutional retrospective study was conducted to investigate clinical features and prognostic factors in patients older than 40 years with osteosarcoma. Methods: Patients with conventional high-grade osteosarcoma older than 40 years were recruited to this study. Secondary osteosarcoma arising from Paget's disease or irradiated bones was excluded. Information on tumor- and treatment-related factors was collected and statistically analyzed. The median follow-up was 57 months (range 8-244 months) for all surviving patients. Results: A total of 86 patients were enrolled in this study. The median age at diagnosis was 61 years. Surgery and chemotherapy were conducted in 73 and 63 % of all patients, respectively. The 5-year overall and event-free survival rates were 38.8 and 34.0 %, respectively. Tumor site (extremity 57.9 %; axial 19.0 %; p < 0.0001), metastasis at diagnosis (yes 12.2 %; no 48.3 %; p < 0.0091), and definitive surgery (yes 56.2 %; no 10.6 %; p < 0.0001) were associated with overall survival. Although patients without metastasis who received definitive surgery were regarded as good candidates for chemotherapy, the addition of chemotherapy did not have any impact on the outcome (yes 63.4 %; no 65.2 %; p = 0.511). Conclusions: The present study revealed the distinct clinical features, such as the high incidence of truncal tumors or metastasis at diagnosis, in patients older than 40 years with osteosarcoma. Additionally, prognostic factor analyses revealed that tumor site, metastasis at diagnosis, definitive surgery, and surgical margins were significant prognostic factors, whereas chemotherapy did not influence survival.
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