Low-dose cytosine arabinoside (Ara-C) therapy in the myelodysplastic syndromes and acute leukemia.

Twenty-two patients with either a myelodysplastic syndrome or acute nonlymphocytic leukemia were treated with 10-21 days of subcutaneous cytosine arabinoside (Ara-C) (5-10 mg/m2 every 12 hours). There were two complete remissions and ten partial responses. Clinically significant improvements in peripheral blood counts persisted for periods of 8 weeks to greater than 21 weeks. Responses were seen even in patients who had previously proven refractory to conventional induction regimens or high-dose Ara-C. The toxicity, however, was considerable. Nearly all patients developed significant thrombocytopenia. Platelet and red cell transfusion support was required in many cases. The response to low-dose Ara-C therapy seen in patients with the leukemic and myelodysplastic disorders may be mediated by the induction of cell differentiation or a direct cytotoxic effect on a sensitive population of cells. Low-dose Ara-C may provide an alternative therapy in the selected patient with acute nonlymphocytic leukemia or a myelodysplastic syndrome.