This study will enroll approximately 3000 CP-CML patients that must have a history of at least 4 years of TKI treatment and at least 18 months of DMR. Events developing in patients after the end of discontinuation and TKI resumption will be considered as linked to the discontinuation if they will develop within 36 months from the end of discontinuation. This rule will apply also to subsequent TD attempts. In case of a second or subsequent discontinuation attempt after the failure of a previous one (for molecular relapse), patients must have re-achieved a DMR with TKI therapy resumption and must keep DMR for at least 18 months before another TD.~Collection of data will be retrospective and prospective, as each center will collect the data for 24 months. Patients who discontinued before the opening of this study will contribute to the retrospective cohort, while those who will discontinue after it will contribute to the prospective cohort. Patients who discontinued before the opening of this study but will continue their discontinuation after it, will contribute to both cohorts. For patients prospectively recruited, monitoring of disease status will be performed to assess the maintenance of the molecular remission during the study period.~Patients with an atypical BCR-ABL1 fusion gene, which does not allow the use of Q-RT-PCR, will be monitored by qualitative PCR and will be analyzed separately. For these patients, negativity of nested qualitative RT-PCR will be considered a surrogate of DMR of patients monitored by Q-RT-PCR, while loss of negativity of first-round qualitative PCR will be considered a surrogate of loss of MMR (i.e. molecular relapse). Accordingly, for patients monitored by qualitative PCR, TKI resumption after TD will be provided in case of a new positivity of first-round PCR.~.
The purpose of this study is to investigate the safety profile of TKI discontinuation in clinical practice, with particular regard on the risk of progression after treatment discontinuation.