To the best of our knowledge, no study has reported a significant difference in driver mutations frequency in prePMF and ET cases, while in our cohort we observed a higher incidence of CALR mutations among prePMF cases, compared to ET, that might explain, at least in part, the differences in platelet counts and in the occurrence of extreme thrombocytosis. The gene discussed is CALR; the disease is essential thrombocythemia.