Prognostic Effect of Diaphyseal Location in Osteosarcoma: A Cohort Case-Control Study at a Single Institute

Little is known about the clinical outcome or prognosis of diaphyseal osteosarcoma treated with modern therapeutic strategies. We conducted both cohort (n = 400) and case-control (n = 102) studies on 34 American Joint Committee on Cancer stage II diaphyseal osteosarcomas of the extremities. In the cohort study, 34 patients with a diaphyseal osteosarcoma showed significantly better survival than 366 patients with metaphyseal osteosarcoma (5-year metastasis-free survival rates, 87% for cases vs. 59% for controls, P = 0.01; 5-year overall survival rates, 90% for cases vs. 71% for controls, P = 0.04). The case-control study conducted on 34 patients with diaphyseal osteosarcoma and 68 controls (recruited from among the 366 patients with metaphyseal osteosarcoma by matching for age, tumor volume, and location) showed no survival difference between cases and controls (5-year metastasis- free survival rates, P = 0.07; 5-year overall survival rates, P = 0.26). Location differences between the diaphysis and metaphysis may have no prognostic relevance.