Survival and risk of leukaemia in polycythaemia vera and essential thrombocythaemia treated with oral radiophosphorus: are safer drugs available?

For 366 patients with polycythaemia vera (PV) or essential thrombocythaemia (ET) diagnosed 1971-1990, oral administration of 32-P was used as myelosuppressive treatment. Retreatment was not restricted to any defined interval and the number of treatments or the total dose were not limited. For 107 patients, follow-up was > 10 years. 15 of these presented with life-threatening occlusive vascular symptoms and their survival was short. For the remaining 92 patients 5-yr survival was not significantly worse than for a Swedish population matched for age and sex. Survival at 10 yr was lower, 51% versus 66% expected. Acute myeloid leukaemia (AML) was diagnosed in 11 of the 107 patients (10.3%). In the whole material of 366 patients, 17 have developed AML with a median time of 8.5 yr from start of treatment. There was a maximum incidence of 4% per yr after 8-12 yr. Later, the incidence decreased. The median annual dose of 32-P for the AML patients was 100 MBq and was not significantly larger than for a matched control group surviving without AML, 96 MBq. The results are compared with reports on PV or ET patients treated with busulphan (Bu) or hydroxyurea (HU). With comparable periods of follow-up there are no indications that an adequate myelosuppression with oral 32-P will be associated with shorter survival or higher incidence of AML than treatment with Bu or HU. It is concluded that, for the time being, oral administration of 32-P is an acceptable standard treatment in PV and ET.