Endogenous erythroid clones (EEC) in polycythaemia and their relationship to diagnosis and the response to treatment.

The growth in culture of circulating erythroid progenitors (BFU-e) from 34 patients with erythrocytosis was evaluated together with the clinical and bone marrow features at presentation and the subsequent response to treatment. Clonal erythroid growth in vitro in the absence of added erythropoietin (EEC) was observed in 17/18 patients with clinically unequivocal polycythaemia vera and in these patients bone marrow morphology was also abnormal. EEC were also present in three out of five patients with only a single minor criterion of that disease but none of the 11 patients without major or minor criteria or evidence of secondary polycythaemia were EEC positive. This group had a very low incidence of bone marrow abnormalities, was probably heterogenous in nature and included two patients with elevated serum immunoreactive erythropoietin of unknown cause. The reduction in haematocrit following treatment was assessed in EEC positive and negative patients and was found to be inferior in those lacking EEC. Thus both the poor therapeutic response and the low incidence of bone marrow abnormalities in patients lacking any other clinical features of polycythaemia vera correlated closely with the absence of EEC in in vitro culture. Myeloproliferative disorder may therefore be an unlikely cause of the erythrocytosis in such individuals.