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Keywords:

  • chronic myeloproliferative disorders;
  • essential thrombocythaemia;
  • hydroxyurea;
  • busulphan;
  • secondary leukaemia

We have previously demonstrated that hydroxyurea (HU) reduces the rate of vascular complications in patients with essential thrombocythaemia (ET) at high risk of thrombosis. However, the relatively short follow-up (median 27 months) did not enable the evaluation of the risk of developing secondary malignancies. In this study, we report the long-term outcome of the 114 patients included in the trial: 56 patients randomized to receive HU and 58 patients to receive no cytoreductive therapy. Before randomization, 15 patients had been treated with busulphan. During the observation period, 29 patients (50%) shifted from the control to the HU group mainly because of thrombosis. Median follow-up was 73 months (range 3–94). Analysis was by intention to treat and, when indicated, by treatment.

When analysed by intention to treat, 46 out of 54 patients (85%) originally randomized in the HU group are alive, compared with 49 of 58 patients (84%) in the control group [not significant (n.s.)]. Five patients (9%) in the HU group and 26 patients (45%) in the control group had thrombosis (P < 0·0001). Seven patients (13%) in the HU group developed secondary acute leukaemia, myelodysplastic syndromes or solid tumours, compared with only one of the control group patients (1·7%) (P = 0·032). The occurrence of secondary malignancies was also analysed by treatment: none of the 20 patients who had never been treated with chemotherapy developed neoplasia vs. three of the 77 patients given HU only (3·9% n.s.) and five of the 15 patients given busulphan plus HU (33% P < 0·0001).

This study showed that: (a) HU reduced the risk of thrombosis in ET patients; (b) the sequential use of busulphan and HU significantly increased the risk of second malignancies; and (c) overall survival was not affected by HU therapy.