(P 159) CHONDROSARCOMA IN JAPAN: A POPULATION-BASED ANALYSIS USING NATIONAL CANCER REGISTRY

Objective: Chondrosarcoma is a rare malignant bone tumor with diverse histological features. This study investigated epidemiological characteristics, clinical features, prognostic factors, and subtype differences of chondrosarcoma in Japan using National Cancer Registry data.

Methods: We analyzed chondrosarcoma cases diagnosed 2016-2019 from Japan's National Cancer Registry covering the entire population. Cases were identified using ICD-O-3 codes. We calculated age-adjusted incidence, estimated survival using Kaplan-Meier methods, and identified prognostic factors through multivariate Cox regression. Subtype characteristics were compared among conventional, dedifferentiated, mesenchymal, clear cell, and other variants.

Results: We identified 1,015 cases with age-adjusted incidence 0.159 per 100,000. The cohort comprised 558 men (55%) and 457 women (45%), 84% aged ≥40 years. Common locations were extremities (45.9%) and chest wall (23.8%). Conventional type was predominant (84.7%), followed by dedifferentiated (6.7%), mesenchymal (2.9%), and clear cell (2.5%). Overall 1-year and 3-year survival were 90% and 76.2%. Multivariate analysis revealed female sex (HR 0.531, p=0.001), age 15-39 years (HR 0.163, p< 0.001), non-dedifferentiated subtypes, localized disease, and surgery as favorable factors. Subtype differences included younger age for mesenchymal and clear cell variants and higher metastases in dedifferentiated (18%) and mesenchymal (21%) types.

Conclusion: This first nationwide chondrosarcoma analysis in Japan provides comprehensive epidemiological data and identifies key prognostic factors. Findings demonstrate significant subtype heterogeneity and highlight individualized management importance. These data establish foundation for future clinical trial design and patient stratification in Japan.