MPL and myeloproliferative disorder: The latter two share common molecular and morphologic traits with ET, including JAK2, CALR, and MPL mutations (also known as MPN driver mutations); these mutations are mutually exclusive, for the most part, and their frequencies in ET are ~60% for JAK2, 25% for CALR, and 3% for MPL; of note, these three driver mutations might not be detected in ~10–15% of patients with ET, henceforth referred to as triple-negative ET [1, 3].