In this issue of Blood, 2 groups-Thoennissen et al and Beer et al-using complementary approaches address the genetic basis for LT in MPDs, PV, ET, and PMF. Leukemic transformation (LT) is the most serious complication of myeloproliferative disorders (MPDs). For polycythemia vera (PV), a minimum spontaneous transformation rate of 1.5% has been established. Prospective studies of adequate duration are lacking for essential thrombocytosis (ET) but LT is un- likely to be more frequent. For primary my-elofibrosis (PMF), however, an LT rate of 15% has been recorded. Treatment-induced acute leukemia (t-AL) occurs at a much higher rate in PV, but adequate prospective studies are lacking for ET and PMF. The mechanisms for t-AL are understood, but whether these apply to hydroxyurea as they do for other types of chemotherapy is still controversial.
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