Retrospective multicenter study on the development of peripheral lymphocytosis following second-line dasatinib therapy for chronic myeloid leukemia.

The current retrospective study investigated the incidence of lymphocytosis following second-line dasatinib therapy in chronic myeloid leukemia (CML) and analyzed the clinical factors predictive of the development of lymphocytosis, as well as association with treatment outcomes. Fifty CML patients who failed imatinib treatment and received dasatinib were included from nine centers in the Republic of Korea. The cumulative incidence of lymphocytosis was assessed, and cytogenetic and molecular response, treatment failure, loss of response, progression to advanced disease, and survival were evaluated and analyzed according to the development of lymphocytosis. After a median of 17 months of dasatinib therapy, 23 patients (46%) developed lymphocytosis (median onset 4 months). No clinical predictive factor for the development of lymphocytosis was found. The group presenting lymphocytosis showed a higher complete cytogenetic response (CCyR; 78.3 vs. 29.6%, P = 0.001) and major molecular response (MMR; 52.2 vs. 14.8%, P = 0.005), in comparison to the group without presenting lymphocytosis. The development of lymphocytosis after dasatinib was identified as a favorable independent marker for predicting a CCyR (P = 0.002) or MMR (P = 0.003). Further study is necessary to identify which subset of lymphocytes was expanded and to reveal the exact mechanism by which dasatinib induces lymphocyte expansion.