Clonality Assay (X-CIP) and JAK 2 V617P Mutation: Clustering Patients with Essential Thrombocythemia at High Risk for Thrombosis.

We have previously demonstrated that clonal hemopoiesis in female ET patients was significantly associated to the risk of thrombosis. When data on JAK2 V617P mutation became available we aimed to evaluate the incidence of this mutation according to clonality status. Ninety-two female patients, median age 32 (19–65) with a diagnosis of ET according to PVSG criteria were studied for clonality with X-CIP, 83 patients were evaluable for endogenous erythroid colonies (EECs) growth and 44 patients were evaluable for JAK2 V617P mutation. Twenty episodes of thromboses (21.7%) were detected and they include splanchnic (11), CNS (5), limb (3) thromboses and pulmonary embolism (1). Thromboses were mainly detected at diagnosis. Thirthy-seven patients showed clonal hemopoiesis (40%), 27 had polyclonal hemopoiesis (29.5%) and 28 were considered uninterpretable due to constitutional skewing (30.5%). Thromboses were overrepresented in the monoclonal group in respect to the polyclonal one (15/37 vs 2/27, p=0.003). DNA for analysis of JAK2 V617P by allele-specific PCR was available for 44 of these patients. Thirty-two patients of 44 (73%) showed JAK2 V617P mutation; JAK2 V617P was found in 16/21 patients with monoclonal hemopoiesis (76%), in 9/13 in the polyclonal group (69%) and in 7/10 (70%) in patients with constitutional skewing. Thirteen of the 32 patients with JAK2 V617P mutation (41%) had thromboses while no thrombotic event was recorded in wild type patients (p=0.008); among the 13 patients with thrombosis and JAK2 V617P mutation, 9 (69%) had monoclonal hemopoiesis, 2 (15%) had polyclonal hemopoiesis, and 2 had constitutive skewing. Thus there was a significant increase in thrombotic events in patients with JAK2 V617P mutation and monoclonal hemopoiesis (p=0.04). JAK2 V617P mutation was also significantly associated to the presence of EECs (p=0.02); in fact 22/26 patients with EECs growth showed JAK2 mutation (85%). Finally when patients with splanchnic thromboses were analyzed 9/11 had a monoclonal X-CIP (81.8%) and 7 of them who were evaluable for JAK2 V617P mutation were invariably carriers of the mutation. Thus we confirm that X-CIP in young female ET is correlated to the risk of thrombosis. JAK2 V617P mutation is significantly associated to the development of thrombosis and is present in the vast majority of patients with monoclonal hemopoiesis. The mechanisms underlying monoclonal hemopoiesis in the absence of JAK2 V617P mutation are unclear, notwithstanding these patients are clinically characterized by both absence of EECs and thrombosis.