Close to one-third of patients with chronic myelogenous leukemia (CML) treated with the tyrosine kinase inhibitor dasatinib developed persistent lymphocytosis, and these patients were more likely to achieve complete disease response and have longer response durations, according to a study published in Cancer.1

According to study researcher Charles A. Schiffer, MD, of Barbara Ann Karmanos Cancer Institute in Detroit MI, several other small studies of dasatinib in patients with CML had shown an increase in the number of T cells or natural killer (T/NK) cells after therapy was initiated.

“There was the suggestion that some patients with advanced disease who had this T/NK proliferation might have done better than expected,” Schiffer told Cancer Therapy Advisor. “With about 6 to 7 articles showing this trend, it seemed appropriate to look and see if this finding could be confirmed in a larger trial.”

Schiffer and colleagues collected data from 3 large clinical trials on 1402 dasatinib-treated patients with CML in chronic phase (CML-CP), CML-CP refractory/intolerant to imatinib, or with CML in accelerated or myeloid-phase. They analyzed if the occurrence of lymphocytosis was associated with disease response, survival, or side effects.

“We looked at people with elevated lymphocyte counts, making the reasonable assumption that people with elevated counts were patients who had T/NK proliferation,” Schiffer said.

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Lymphocytosis occurred in 32% to 35% of patients across all the phases of CML, and the lymphocytosis persisted for 12 months or longer in at least half of these patients. The researchers found no difference in the occurrence of lymphocytosis related to the dose of dasatinib, and no significant lymphocytosis in patients treated with imatinib.