Changes in the characteristics of the bone marrow during therapy for acute non-lymphocytic leukemia: relationship to response to remission induction therapy.

The bone marrows of patients with acute non-lymphocytic leukemia being treated with 'high dose' cytosine arabinoside remission induction therapy were sampled prior to the initiation of chemotherapy, after 6 days of therapy and again 7 days after the conclusion of therapy. These studies demonstrated that the marrows of patients who would enter remission (CR patients) contained less leukemic cells prior to therapy than patients who would fail to enter remission because of persistent leukemia (resistant disease, or RD patients). A comparison of the day 6 and 7-day post-therapy marrows with the pretherapy marrow demonstrated that while the % reduction in leukemic cells was greater for CR patients than for RD patients, the absolute reduction in leukemic cell mass was the same for both groups. While there was no relationship between the percentage of cells in S phase and the pretherapy leukemic cell mass, the greater the pretherapy leukemic cell mass the greater the likelihood that the leukemic cells would be resistant to the metabolic effects of cytosine arabinoside in vitro.