A lower dosage of imatinib is sufficient to maintain undetectable disease in patients with chronic myeloid leukemia with long-term low-grade toxicity of the treatment.

The information about chronic myeloid leukemia (CML) patients with a deep molecular response of ≥ 4.5 log reduction (MR4.5) in whom the dose of imatinib (IM) had to be reduced to relieve toxicity is insufficient. In 205 CML patients the dose of IM was reduced in 19 (31.2%) out of 61 patients with MR4.5. The patients (12 pretreated with interferon-alpha) achieved MR4.5 after an average of 27.7 months. The duration of MR4.5 before the reduction of the dose was 16-123 (mean = 56.7) months. After the IM reduction (200 mg daily to 400 mg twice weekly for 15-90 (mean = 48) months) MR4.5 or major molecular response (MMR) was maintained in 14 (73.7%) and 2 (10.5%) patients, respectively. Three patients who lost MMR (15.8%) after the discontinuation of IM regained MR4.5 after the reintroduction of a lower dose. A lower dosage of IM should be tested for the management of side effects in patients with MR4.5 in prospective studies.