Why are there so few randomized trials for patients with primary refractory acute myeloid leukemia?

Fewer patients with primary refractory AML ("PREF") are entered into phase 3 trials than are patients with relapsed AML. This is particularly noteworthy because data from phase 3 trials for newly diagnosed AML indicated PREF and relapse are equally common. Here I discuss three possible reasons for this discrepancy. First, there is disagreement whether the criterion for PREF AML should be failure of one or two courses of initial induction therapy. Second, there may be an impression that PREF AML is qualitatively worse than relapsed AML. Third, there may be a general unwillingness to randomize patients with such poor prognoses.