JAK2 and essential thrombocythemia: Platelet count is significantly higher in type II vs type I CALR mut ET patients, but no difference was noted in thrombosis-free survival in a study with a large cohort of ET patients. However, there is a significant survival difference in the setting of PMF, as CARL type-I positive PMF patients do much better than CALR type-II or JAK2 (V617F) positive PMF patients (84).