Cumulative incidence of thrombosis in PMF patients stratified according to their driver mutation. Vertical tick marks indicate right-censored patients. JAK2-mutant patients had a higher incidence of thrombosis than those with CALR mutation (P = .021). This difference remained statistically significant after adjusting for age (SHR, 2.19; 95% CI, 1.15-4.18; P = .017), the estimated risk of thrombosis being about 2-fold in JAK2-mutant compared with CALR-mutant patients.