Study Cohort
We identified patients aged ≤ 25 years with CCS, epithelioid, and synovial sarcomas as classified by ICD-O-3 codes. Patients were included only if they underwent primary surgical resection or primary site radiation for local control of their tumor. Lymph node metastasis (present vs. absent) was defined using pathologic N-stage and NAACCR Item 820 for regional lymph nodes positive. We excluded patients with documented late entries (n=20), multiple primary tumors (n=48), and unknown lymph node sampling status (n=19), which we defined as a binary variable based on documentation of regional nodal examination or surgery (NAACCR Items 830, 1292).15 We used multiple imputation by predictive means matching to resolve residual missing values in the dataset.