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.