Efficacy of low-dose imatinib in chronic-phase chronic myelogenous leukemia patients

Imatinib mesylate is very effective in the treatment of chronic myelogenous leukemia (CML) and 400 mg/day imatinib is considered the standard treatment dose for chronic-phase (CP) patients. However, despite its relative tolerability, some patients require a lower dosage or temporary cessation of treatment because of severe adverse events. It remains unclear whether reduced-dose imatinib is as effective as the standard dose in achieving and maintaining a major molecular response (MMolR), an important goal of imatinib therapy. In this study, Japanese patients with CML-CP, as classified by their Sokal scores, were treated with imatinib. MMolR was observed in all patients with low Sokal scores who were treated with 300 or 400 mg/day imatinib, suggesting that low scores predict favorable response to treatment even at lower dosages, which is preferable since it is associated with fewer adverse events. Low-dose therapy also achieved MMolR in patients with intermediate or high scores. However, loss of complete cytogenetic response (CCgR) or an increase in BCR-ABL transcripts was noted shortly after these patients achieved CCgR, suggesting that a CCgR short of MMolR still indicated a risk of loss of response in these risk categories. MMolR was maintained in these patients by timely increases in dosage. Achieving CCgR within 12 months and maintaining it without an increase in BCR-ABL transcripts might indicate that low-dose imatinib therapy can produce acceptable outcomes without excess toxicity.