Dasatinib cessation after deep molecular response exceeding 2 years and natural killer cell transition during dasatinib consolidation

Tyrosine kinase inhibitors (TKI) improve the prognosis of patients with chronic myelogenous leukemia (CML) by inducing substantial deep molecular responses (DMR); some patients have successfully discontinued TKI therapy after maintaining DMR for ≥1 year. In this cessation study, we investigated the optimal conditions for dasatinib discontinuation in patients who maintained DMR for ≥2 years. This study included 54 patients with CML who were enrolled in a D-STOP multicenter prospective trial, had achieved DMR, and had discontinued dasatinib after 2-year consolidation. Peripheral lymphocyte profiles were analyzed by flow cytometry. The estimated 12-month treatment-free survival (TFS) was 62.9% (95% confidence interval: 48.5%-74.2%). During dasatinib consolidation, the percentage of total lymphocytes and numbers of CD3- CD56+ natural killer (NK) cells, CD16+ CD56+ NK cells and CD56+ CD57+ NK-large granular lymphocytes (LGL) were significantly higher in patients with molecular relapse after discontinuation but remained unchanged in patients without molecular relapse for >7 months. At the end of consolidation, patients whose total lymphocytes comprised <41% CD3- CD56+ NK cells, <35% CD16+ CD56+ NK cells, or <27% CD56+ CD57+ NK-LGL cells had higher TFS relative to other patients (77% vs 18%; P < .0008; 76% vs 10%; P < .0001; 84% vs 46%; P = .0059, respectively). The increase in the number of these NK cells occurred only during dasatinib consolidation. In patients with DMR, dasatinib discontinuation after 2-year consolidation can lead to high TFS. This outcome depends significantly on a smaller increase in NK cells during dasatinib consolidation.