Cumulative incidence of polycythemic transformation, thrombotic events, myelofibrotic transformation, and leukemic transformation in patients with CALR- or JAK2-mutated ET and in those with PV. The cumulative incidences were estimated with a competing risk approach, considering death for all causes as a competing event.24 (A) In patients with JAK2-mutated ET, the cumulative incidence of polycythemic transformation was 28.6% (95% CI 20.7-37.0) at 15 years. No progression to PV was observed in patients with CALR-mutated ET. (B) Patients with CALR-mutated ET showed a lower incidence of thrombosis than those with JAK2-mutated ET (10.5% vs 25.1% at 15 years, P = .001), or those with PV (10.5% vs 34.7% at 15 years, P < .001). By contrast, patients with JAK2-mutated ET and those with PV did not differ in terms of cumulative incidence of thrombosis (P = .314). These differences in risk of thrombosis remained statistically significant even after adjusting for age, as detailed in the text. (C) The 15-year cumulative incidence of myelofibrotic transformation was 13.4% (CI 95% 5.4-25.2) in CALR-mutated ET, 8.4% (CI 95% 3.9-15.3) in JAK2-mutated ET, and 13.6% (CI 95% 7.3-21.9) in PV, without any significant difference among these 3 subgroups even after adjusting for age. (D) The 15-year cumulative incidence of leukemic transformation was 2.5% (CI 95% 0.2-11.3) in CALR-mutated ET, 4.3% (CI 95% 1.9-8.2) in JAK2-mutated ET, and 14.6% (CI 95% 8.4-22.3) in PV. Although CALR-mutated patients showed a lower risk of leukemic transformation in comparison with both those with JAK2-mutated ET (P = .026) and those with PV (P < .001), no significant difference was observed after adjusting for age.
