Survival improvement and widening social disadvantage-related disparities in osteosarcoma: a Surveillance, Epidemiology, and End Results-based retrospective cohort study.

Background: Evidence on contemporary survival trends and social disadvantage-related disparities in osteosarcoma remains limited due to its rarity. According to the theory of fundamental causes, socially advantaged populations may benefit more from medical progress, potentially widening survival disparities over time. This study aimed to evaluate temporal trends in survival among patients with osteosarcoma and to examine whether survival gains and survival disparities differed across social disadvantage risk groups. Methods: Patients diagnosed with osteosarcoma between 2000 and 2019 were identified from the Surveillance, Epidemiology, and End Results (SEER) database. Overall survival (OS) and cancer-specific survival (CSS) were evaluated across diagnostic periods using Kaplan-Meier methods and multivariable Cox regression. A social disadvantage risk score was constructed based on sex, race, household income, and residence, and patients were classified into low- and high-risk groups. Differences in survival gains and temporal changes in survival disparities between these groups were assessed. Results: A total of 4,381 patients were included; most patients were younger than 40 years (72.1%) and had non-metastatic disease at diagnosis (57.9%). Compared with patients diagnosed in 2000-2004, those diagnosed in 2015-2019 had better OS [hazard ratio (HR) =0.79, 95% confidence interval (CI), 0.64-0.94, P=0.001] and CSS (HR =0.76, 95% CI: 0.63-0.92, P<0.001). Male sex, non-White race, lower income, and rural residence were associated with poorer survival. Based on these factors, 2,523 patients were classified as low social disadvantage risk and 1,858 as high social disadvantage risk. Survival gains were greater in the low-risk group than in the high-risk group (OS: P for interaction=0.002; CSS: P for interaction=0.004). CSS disparities between groups widened significantly over time (P for interaction=0.048), with a similar but non-significant trend for OS (P for interaction=0.10). Conclusions: Survival among patients with osteosarcoma improved modestly between 2000 and 2019, but these gains were not equally distributed. Patients with lower social disadvantage risk experienced greater survival improvements, contributing to widening survival disparities. Efforts to improve equitable access to timely diagnosis, specialized sarcoma care, and supportive services are needed to reduce these disparities.