The Significance of Myelosuppression during Therapy with Imatinib Mesylate in Patients with Chronic Myelogenous Leukemia in Chronic Phase

BACKGROUND. Imatinib mesylate induces high rates of hematologic and cytogenetic response in patients with chronic myelogenous leukemia (CML). During therapy with imatinib, up to 45% of patients with CML reportedly experience myelosuppression ≥ Grade 3, requiring interruption of therapy and/or dose reductions. The significance of myelosuppression for response to imatinib is unknown. METHODS. The authors analyzed 143 patients with late chronic-phase CML who were treated with imatinib after failing interferon. Univariate and multivariate analyses were performed to determine patient characteristics that were correlated with myelosuppression response and the association between myelosuppression and cytogenetic response. RESULTS. Neutropenia ≥ Grade 3 (according to National Cancer Institute Common Toxicity Criteria) occurred in 64 patients (45%), and thrombocytopenia ≥ Grade 3 occurred in 31 patients (22%). Any myelosuppression ≥ Grade 3 was associated with a lower rate of major (P = 0.04) or complete (P = 0.01) cytogenetic responses. This was more pronounced with myelosuppression that lasted > 2 weeks. The major cytogenetic response rate was 58% with Grade ≥ 3 myelosuppression compared with a rate of 75% without Grade ≥3 myelosuppression (P = 0.03); the complete cytogenetic response rates were 36% and 63%, respectively (P = 0.001). In a multivariate analysis, pretreatment platelet count, imatinib dose reductions, and duration of myelosuppression were associated significantly with response. CONCLUSIONS. Myelosuppression is an independent adverse factor for achieving cytogenetic response with imatinib in patients with CML. Intervention with hematopoietic growth factors in patients with CML who are treated with imatinib should be investigated.