Erythroid colony formation in primary thrombocythaemia: evidence of hypersensitivity to erythropoietin.

In a group of 14 patients with primary thrombocythaemia (PT) the study of erythropoietic colony formation in vitro showed the development of so-called 'endogenous' colonies, namely colonies with no added erythropoietin (Ep), in all but one case. In the presence of added Ep the colony formation increased slightly in the PT group, but the rise in the control group was so pronounced that any statistical difference between the two groups disappeared. No 'endogenous' colonies were observed in cases of secondary thrombocytosis. This finding reinforces the view that PT is a myeloproliferative disorder and establishes that some erythroid progenitors show the same high sensitivity to Ep as that found in polycythaemia vera; it is of interest that, in the patients studied, there was no apparent involvement of erythropoiesis.