2.2 Statistical methods
Baseline variables were analyzed by descriptive statistics. For survival
analysis, an event was defined as relapse, progression, abandonment,
second malignant neoplasm or death due to any cause. Event-free survival
(EFS) was calculated as time from the date of diagnosis to event.
Overall survival (OS) was calculated as time from date of diagnosis to
death due to any cause. All patients without an event were censored at
last follow up. Estimates of survival were computed using the
Kaplan-Meier method. The Hazard Ratios (HR) and significance associated
with patient characteristics were assessed in a Cox proportional hazards
regression model. Log-rank test was used for comparing survival. A p
value ≤0.05 was considered significant. Statistical analysis was
performed using STATA software, version 15.1. Pearson’s Chi-square and
Mann-Whitney U test were used for assessing associations between
clinical parameters and necrosis. An optimal cutoff for Tumor Necrosis
with respect to EFS and OS was chosen in this study for outcome
analysis. Here, we optimized the cutoff by maximizing the significance
assessed by the log-rank test.