2.3. Statistical analysis
Survival time was calculated from the date of diagnosis to the time of
event or last follow-up. Tumor progression, relapse, occurrence of
second malignancy, or death due to any cause were considered for event
free survival (EFS). Overall survival (OS) was measured from the date of
diagnosis to death from any cause. Patients still alive at the end of
the study were censored at the date of the last observation. Survival
probability was calculated by the Kaplan-Meier method and heterogeneity
in survival among strata of selected variables was assessed with the
Log-Rank test [14]. Five-year EFS and OS were reported along with
their 95% confidence intervals (CI) as computed using the Peto-Peto
method [15]. The Cox proportional hazards models were fit to compare
EFS and OS while adjusting for potential confounders. Categorical
variables were reported as counts and percentages and compared using
Fisher’s Exact test. All data analyses were performed using the SAS
statistical package (SAS, release 9.4; SAS Institute Inc., Cary, NC,
USA).