Age-Related Differences in Outcomes and Tumor Characteristics of Ultrarare Sarcomas: A Nationwide Study

Ultrarare sarcomas (URS) are subtypes of sarcomas with an extremely low incidence (≤1 per 1,000,000), resulting in limited clinical understanding. This study aimed to investigate the clinical characteristics, overall survival (OS) outcomes, and prognostic factors of URS by using a national cancer registry database.

Patients in the Taiwan Cancer Registry, diagnosed between January 2002 and December 2019, were included. Based on the International Classification of Diseases for Oncology, Third Edition, histologic codes and their incidence, patients were categorized into URS, non-URS (NURS), or non-sarcoma solid tumors (NSST). Annual percentage change (APC) and factors associated with OS were analyzed.

Among 1,578,049 patients, 0.23% (n = 3,690) were URS, 1.93% (n = 30,503) were NURS, and 97.83% (n = 1,543,856) were NSST. The most common URS histologies were conventional chordoma and extraskeletal Ewing sarcoma. The incidence of URS demonstrated an increase from 2002 to 2019 (APC = 2), without an improvement in OS [2011-2019 vs. 2002-2009 URS: HR, 1.12; 95% confidence interval (CI), 1.02-1.20]. After multivariable adjustment, OS remained worse in URS compared with NURS (HR, 1.86; 95% CI, 1.77-1.96). Across all age groups except 0 to 18 years, patients with URS had inferior OS to those with NURS. Notably, within individual URS histologies, age was independently associated with OS.

Despite an increasing incidence, outcomes for URSs remain poor. Age emerges as a major determinant of heterogeneity and prognosis, underscoring the need for age-stratified approaches in future research and clinical management.

Our findings underscore the urgent need for increased awareness of URS and characterize the impact of age on these patients. See related In the Spotlight, p. 1487.