In the second patient (female ET), who experienced multiple pulmonary embolism events during the disease, we observed increasing VAF of JAK2 p.Val617Phe driver mutation, from 7,14% at diagnosis to 43,32% at follow-up, despite being on cytoreductive treatment with hydroxyurea, later in combination with anagrelide. Here, JAK2 is linked to essential thrombocythemia.