Circulating erythroid progenitors in patients with ‘spent’polycythaemia vera and myelofibrosis with myeloid metaplasia

Summary. The ability of circulating progenitor cells from patients with polycythaemia vera (PV) and myelofibrosis with myeloid metaplasia (MMM) to develop erythroid colonies was studied in cultures with and without erythropoietin. In all normal controls, patients with secondary polycythaemia and MMM, erythroid colonies developed only after the addition of erythropoietin. Only in patients with PV, both in the active and spent phases of the disease, erythroid colonies developed in the absence of erythropoietin. The results indicate the perpetuation of erythropoietindependent, as well as erythropoietin‐independent progenitors in both phases of this disease. Although spent PV often clinically resembles MMM, there is a basic difference in the behaviour of the circulating erythroid progenitors in these diseases which may serve as a useful tool in discriminating MMM from spent PV, when there is no history of active PV.