[A trial for prolongation of chronic phase of chronic myeloid leukemia--maintenance of leukocyte counts within normal range with busulfan].

To prolong the survival of patients with chronic myeloid leukemia (CML), 19 patients were treated with busulfan to keep their leukocyte counts within normal range by controlling bone marrow hyperplasia. The duration of chronic phase in these patients was significantly longer than that in historical controls who were treated conventionally with busulfan. This prolongation was not ascribable to the difference in such prognostic factors between the two therapy groups as splenomegaly, leukocyte count and percentage of peripheral blasts. There was a significant difference again in the duration of chronic phase between the two therapy group even when restricted to each 11 patients with intermediate relative risk (0.7-1.5) according to Sokal et al. Four patients showed thrombocytopenia less than 5 x 10(4)/microliters, but all these patients recovered within 4 months and there was no further critical side effect except subcutaneous bleeding. This study suggests that maintenance of leukocyte count within normal range and suppression of granuloid hyperplasia in bone marrow with busulfan may prolong chronic phase of CML. Probability of clonal evolution may be decreased by reducing the total leukemic cell mass and suppressing cellular turnover of primitive CML stem cells. Another possibility is that prolongation of chronic phase might be dependent on the appearance of normal karyotype clone after long-term bone marrow suppression just like after intensive chemotherapy or alpha-interferon therapy.