Randomized clinical trial of cystosine arabinoside and 6-thioguanine in remission induction and consolidation of adult nonlymphocytic acute leukemia

One hundred and forty-seven adults with acute nonlymphocytic leukemia were randomized to one of two treatment regimens utilizing cytosine arabinoside and 6-thioguanine. In regimen A the drugs were administered every 12 hours until marrow cellularity was reduced by at least 50%. In regimen B the drugs were administered every 12 hours for 5 days with five to 7 days rest intervals between courses. Decisions to continue or reinstitute therapy were based solely on marrow cellularity and marrow ratings. The overall response in referee-verified cases in both groups was similar (41%); regimen B proved to be the easier protocol to administer but required greater support. Younger patients or those with an initial high hemoglobin count responded best to these drug regimens. Only 36% of our patients experienced severe marrow hypoplasia (i.e., a 75% or greater reduction in marrow cellularity) prior to complete remission, suggesting that cytosine arabinoside and 6-thioguanine in combination may selectively suppress leukemic cells while sparing normal hematopoietic elements.