Preliminary observations on the therapy of the myeloid blast phase of chronic granulocytic leukemia with plicamycin and hydroxyurea.

We observed a dramatic improvement in the peripheral blood counts of a patient in the myeloid blast phase of chronic granulocytic leukemia after plicamycin (mithramycin) therapy of concurrent hypercalcemia. We then treated eight additional patients in the blast phase of chronic granulocytic leukemia with a combination of alternate-day plicamycin and daily hydroxyurea. All six patients with myeloid morphology at the time of blast crisis responded with a return to a chronic phase without an intervening pancytopenic period. Of three patients with lymphoid morphology at the time of treatment, only one responded (this patient had recently relapsed and converted from myeloid to lymphoid morphology). Another patient with nonmyeloid, nonlymphoid blast morphology also did not respond. Continual therapy with the two-drug combination appeared to be necessary, since early relapses were seen in responding patients whose therapy was interrupted. These data are preliminary and will need further confirmation, but they suggest that the combination of alternate-day plicamycin and daily hydroxyurea may be effective in the myeloid blast phase of chronic granulocytic leukemia.