Fig. 1

Overall treatment effects of chemotherapy. a Standard difference in baseline covariates between treated and untreated patients. The covariates of unmatched patients (red dot) represent significant differences between the treated and untreated groups. The treated patients are more likely to be younger and have a larger tumor size and higher SEER stage compared to the untreated patients. Following propensity matching, the covariates are well balanced (black star). b Kaplan–Meier survival curves representing the overall survival rate of patients with SS. The treated group exhibits worse prognoses compared to the untreated group [p = 0.003, hazard ratio: 1.32 (95% CI: 1.10–1.59)]. The x-axis represents time in months. c Kaplan–Meier survival curves of matched patients with SS. The treated group exhibits significantly better prognoses than the untreated group (p = 0.0001). The x-axis represents time in months