High-dose cytosine arabinoside therapy for refractory leukemia

Fifty-seven patients with refractory acute leukemia were treated with high-dose cytosine arabinoside to establish the maximum tolerated dose and duration and to determine the antileukemic activity. The maximum tolerated regimen was found to be 3 g/sq m every 12 hr for 6 days. At this dose, nonhematologic toxicity was limited to conjunctivitis in approximately half of the patients, and liver toxicity (transient elevations in transaminase, alkaline phosphatase, or bilirubin) was frequently observed, but neither was dose-limiting. Extending the duration of treatment to 8 days resulted in excessive diarrhea and skin toxicity (painful erythema with bullae), while increasing the dose to 4.5 g/sq m q. 12 hr for 6 days resulted in severe cerebellar toxicity. Myelosuppression was severe, but was not related to the intensity of treatment; granulocyte recovery occurred a median of 28 days (range 22-40 days) after initiating therapy, and platelet recovery occurred after a median of 25 days (range 16-41 days). Antileukemic activity was evaluable in the 46 patients who survived at least 3 wk. Complete remissions were obtained in 1 of 6 patients with chronic myelogenous leukemia (CML) in accelerated phase and 1 of 3 acute lymphoblastic leukemia (ALL) patients. A more detailed analysis of response was possible for the 37 evaluable patients with acute nonlymphoblastic leukemia: 70% of these patients responded, with 51% complete remissions. The median unmaintained response was 4 mo (range 2-26+ mo). The complete response rate was higher in patients who received at least 12 doses of high-dose cytosine arabinoside compared to shorter regimens 17/28 (61%) versus 2/9 (22%), p less than 0.05. Resistance to cytosine arabinoside in conventional doses was documented in 11 patients, 5 of whom responded (2 complete remissions) to high-dose regimens. We conclude that high-dose cytosine arabinoside in the maximally tolerated regimen of 3 g/sq m every 12 hr for 6 days has substantial antileukemic activity in patients refractory to standard therapy. Durable unmaintained remissions can be achieved, even in patients who fail to respond to cytosine arabinoside in conventional doses.