JAK1 and acquired polycythemia vera: In the last decade, the use of ruxolitinib (a JAK1/2 inhibitor) has been approved as second-line therapy for PV patients, but despite its ability to robustly improve PV-associated symptoms, ruxolitinib does not eliminate the driver mutated clone; whether ruxolitinib alters the course of disease progression remains incompletely defined [4,6,7].