Treatment outcomes and prognosis of osteosarcoma in patients aged 9 years or younger: A study using the nationwide bone tumor registry in Japan.

Abstract

Osteosarcoma is a representative malignant bone tumor that typically occurs in adolescents, with a peak incidence in teenagers. However, osteosarcoma is rare in children younger than 10 years, and its clinical features and prognosis remain unclear. Using data from the nationwide Bone Tumor Registry in Japan, we retrospectively analyzed patients aged ≤19 years diagnosed with osteosarcoma between 2006 and 2019. We compared the clinicopathological characteristics and outcomes between patients aged ≤9 years (group P) and those aged 10-19 years (group A). A total of 1035 patients were included in the study (group P, n = 121; group A, n = 914). The 5-year overall survival (OS) was 73.0 % in group P and 70.7 % in group A (p = 0.84). Among the non-metastatic extremity cases, the 5-year OS rate was 74.5 % in group P and 80.3 % in group A, with no significant difference. The event-free survival rates in surgically treated non-metastatic extremity cases were 60.3 % and 62.4 % in groups P and A, respectively. Amputation was significantly more frequent in group P (18.4 % vs. 7.9 %; p = 0.001). Osteosarcoma in children ≤9 years accounts for approximately 10 % of cases in patients ≤19 years and demonstrates clinical characteristics and prognosis similar to those of adolescents. However, amputations are more frequently performed in younger children, highlighting the need for prosthetic and reconstructive options tailored for this age group.