5-year overall survival according to MTSS. OS for training (A) and validation cohort (B) according to the MTSS risk stratification. The 5-year survival rates according to each cohort and corresponding risk group were 90% (low), 77% (intermediate), 50% (high), and 34% (very high) for the training cohort (n = 205) and 83% (low), 64% (intermediate), 37% (high), and 22% (very high) for the validation cohort (n = 156; P < .001, respectively).