Circulating haematopoietic progenitors in myelofibrosis.

We studied circulating erythroid and granulocyte-monocyte progenitors in 18 patients with idiopathic myelofibrosis and in healthy controls, using the methyl cellulose assay. 9 of the patients had been splenectomized prior to the study. The median number of circulating erythroid burst-forming units (BFU-E) was 8 times higher than that of the controls. 12 patients also had CFU-E (colony-forming unit, erythroid) in the blood. 10 patients had spontaneous BFU-E colony formation, and 8 patients had spontaneous CFU-E colony growth. Granulocyte-monocyte progenitors (CFU-GM) were increased 47 times compared to the controls. There were no differences in colony numbers between splenectomized and non-splenectomized patients. We conclude that in myelofibrosis, circulating erythroid and granulocyte-monocyte progenitors are usually markedly increased in number, but erythroid precursors to a lesser extent than granulocyte-monocyte precursors. Many patients, but not all, show spontaneous erythroid colony formation.