Relationship between the per cent of marrow cells in S phase and the outcome of remission‐induction therapy for acute nonlymphocytic leukaemia

Summary. The relationship between the pretherapy cell cycle characteristics of leukaemic marrow cells and the outcome of remission‐induction therapy for acute nonlymphocytic leukaemia was studied in newly diagnosed and relapsed patients who were then treated with either combination chemotherapy consisting of cytosine arabinoside/anthracycline antibiotic 6 thioguanine or with single agent high‐dose cytosine arabinoside therapy. The outcome of high‐dose cytosine arabinoside therapy was highly dependent upon the per cent of pretherapy cells in S phase with no remissions occurring in patients in whom the ³H‐TdR labelling index was <6%. In contrast, the outcome of cytosine arabinoside/anthracycline antibiotic therapy was independent of the pretherapy cell cycle characteristics of the leukaemic cells.