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.