Primary thrombocythaemia treated with busulphan.

Thirty-seven patients with primary thrombocythaemia (PT) treated with busulphan have been followed for periods up to 25 years. Reduction of the platelet count to less than 400 X 10(9)/l resolved vascular occlusive symptoms, but haemorrhagic symptoms often remained unaltered. Cox regression analysis indicated that there were only two prognostically important presenting features; age had a strong inverse correlation with survival and vascular occlusive symptoms correlated with a better survival. Median duration of survival on treatment was 9 X 8 years. The number of deaths was 2 X 1 times that of a comparable control group, with deaths from myelofibrosis markedly increased. Deaths from thrombosis and malignant diseases, including leukaemia, were not significantly different from the number expected, which emphasizes the efficacy and the relative safety of busulphan for the long-term treatment of PT. Progression of PT into myelofibrosis occurred in 24% of cases and 9% became polycythaemic. Two additional cases of "thrombocythaemia' with a Philadelphia chromosome (and no overt evidence of chronic granulocytic leukaemia) are also presented.