Cytosine arabinoside modulation of the mitotic index in treatment of adult acute leukemia

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Abstract
Twenty‐three unselected adult acute leukemic patients were treated with an initial intravenous pulse of cytosine arabinoside (Ara‐C) 5 mg/kg. The mean mitotic index dropped from 7.7/1,000 to 2.8/1,000 at 4 hours after Ara‐C pulse and rebounded to 6.7/1,000 at 18 hours. Infusions of Ara‐C 7‐10 mg/kg were given for 9 or 12 hours, depending on changes in the mitotic index. The group of responders (M1 or M2 marrows) could be predicted by the initial blast count in the marrow and the change in the mitotic index 18 hours after the Ara‐C pulse. There were 9 (39%) complete and partial remissions. Six patients remained in remission more than 200 days. Since the changes in the mitotic indices induced by Ara‐C were indistinguishable from those of another more successful trial, we infer that factors other than modulation of the cell cycle are critical to the success of this mode of therapy.