The Efficacy of Reduced-dose Dasatinib as a Subsequent Therapy in Patients with Chronic Myeloid Leukemia in the Chronic Phase: The LD-CML Study of the Kanto CML Study Group.

Objective The aim of this study was to prospectively investigate the efficacy and safety profiles of low-dose dasatinib therapy (50 mg once daily). Methods Patients with chronic myeloid leukemia in the chronic phase (CML-CP) who were being treated with low-dose imatinib (≤200 mg/day), but were resistant to this agent were enrolled in the current study (referred to as the LD-CML study). Results There subjects included 9 patients (4 men and 5 women); all were treated with dasatinib at a dose of 50 mg once daily. Among 8 patients who had not experienced major molecular response (MMR; BCR-ABL1 transcript ≤0.1% according to International Scale [IS]) at study enrollment, 5 attained MMR by 12 months. In particular, 3 of 9 patients demonstrated a deep molecular response (DMR; IS ≤0.0069%) by 18 months. Five patients developed lymphocytosis accompanied by cytotoxic lymphocyte predominance. There was no mortality or disease progression, and all continue to receive dasatinib therapy at 18 months with only 2 patients requiring dose reduction. Toxicities were mild-to-moderate, and pleural effusion was observed in 1 patient (grade 1). Conclusion Low-dose dasatinib can attain MMR and DMR without severe toxicity in patients with CML-CP who are unable to achieve MMR with low-dose imatinib. Switching to low-dose dasatinib should therefore be considered for patients in this setting, especially if they are otherwise considering a cessation of treatment.