Deep Molecular Response Rate in Chronic Phase Chronic Myeloid Leukemia: Eligibility to Discontinuation Related to Time to Response and Different Frontline TKI in the Experience of the Gimema Labnet CML National Network.

Background: In the last decade, TKIs improved the overall survival (OS) of chronic myeloid leukemia (CML) patients who achieved a deep and sustained molecular response (DMR, defined as stable MR4 and MR4.5). Those patients may attempt therapy discontinuation. In our analysis, we report the differences in eligibility criteria due to time of response and different TKI used as frontline treatment analyzed in a large cohort of CP-CML patients.
Methods: Data were exported by LabNet CML, a network founded by GIMEMA in 2014. The network standardized and harmonized the molecular methodology among 51 laboratories distributed all over Italy for the diagnosis and molecular residual disease (MRD) monitoring.
Results: Out of 1777 patients analyzed, 774 had all evaluable timepoints (3, 6, and 12 months). At 3 months, 40 patients obtained ≥MR4: of them 14 (3.6%) with imatinib, 8 (5.8%) with dasatinib, and 18 (7.4%) with nilotinib (P = .093); at 6 months, 146 patients were in MR4: 42 (11%) with imatinib, 38 (28%) with dasatinib, and 66 (27%) with nilotinib (P < .001). At 12 months, 231 patients achieved a DMR: 85 (22%) with imatinib, 55 (40%) with dasatinib and 91 (38%) with nilotinib (P < .001). Achieving at least ≥MR2 at 3 months, was predictive of a DMR at any timepoint of observation: with imatinib 67% versus 30% of patients with <MR2, with dasatinib 66% versus 28% of patients with <MR2, and with nilotinib 75% versus 30% of patients with < MR2 (P < .001). At the same time point, achieving at least ≥MR3 is even more predictive of a DMR at any timepoint: 89% versus 38% of patients with <MR3 with imatinib (P < .001), 84% versus 40% of patients with <MR3 with dasatinib (P < .001), and 89% versus 49% of patients with <MR3 with nilotinib (P < .001). Of 908 patients who reached a DMR, 461 (51%) lost it: the loss of response after >2 years was significant for patients who at 3 months had ≥MR2 (18% vs. 9.9% of pts with <MR2, P = .038).
Conclusion: In conclusion, reaching ≥MR2 and a MR3 at 3 months it seems predictive of a DMR at any time point. Considering the prerequisite for a discontinuation with a sustained DMR only a minority of patients can be eligible for the discontinuation, regardless the frontline treatment received.
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