CORRESPONDENCE Leukemic Transformation in Polycythemia Vera To the Editor:

Study Group1 comparing hydroxyurea with pipobroman in the treat-ment of polycythemia vera (PV) makes an important contribution to the debate about the treatment of this condition. We would like to make some observations about the presentation of their results. This particu-larly relates to their statements about the observed actuarial risk of leukemia. The investigators chose, both in the text and the summary, to state that for both drugs ‘‘the risk of leukemia is approximately 10 % at the 13th year.’ ’ This statement may be misleading if it is compared to other studies without presenting confidence intervals for their observa-tion and also appreciating that other studies often quote an overall percentage incidence of leukemia rather than actuarial risk. In their study approximately 27 % and 15 % of the total number of patients involved remained under observation at the 10th and 13th year, respectively. Thus, by the 13th year the number of patients remaining was relatively small and the accuracy of the actuarial risk of leukemia a