SEER Coding and Variable Definitions
Demographic data included age at diagnosis, gender, and race; the latter was categorized into White/Caucasian, Black/African American and other. Tumor characteristics included histologic grade, stage, and size. Based on the study population’s median value of largest tumor dimension in any direction, tumors were categorized into large (>3 cm), small (≤3 cm), and of unknown size. Data on treatment course including surgical resection - other than biopsy, radiation therapy, and chemotherapy were retrieved from the SEER database. The era of diagnosis divided in 10-year intervals (1998-2008 and 2009-2016) was also introduced as a covariate variable.