Comparison of BT rates among 826 Mayo Clinic patients with ET vs PV vs PMF, which includes accounting for death as a competing risk. Cumulative incidences of BT (95% CI) were 0.038 (0.013-0.062) for ET, 0.068 (0.033-0.102) for PV, and 0.142 (0.095-0.186) for PMF; P values were .03 for PV vs PMF at 20 years, .002 for ET vs PMF at 20 years, and .16 for ET vs PV at 20 years.