The principal aim of this study is to evaluate complete molecular remission in patients with chronic myeloid leukemia (CML) in deep molecular response after stopping tyrosine kinase inhibitor (TKI) treatment. The second aim is to characterize the immunological status of patients with CML at the time of TKI interruption and then at 3 months after the interruption.

ARGENTINA STOP TRIAL is a multicentre, open-label, uncontrolled trial to estimate the persistence of molecular remission in patients with chronic phase Chronic Myeloid Leukemia (CML) in Deep Molecular Response after stopping Tyrosine Kinase Inhibitor (TKI)

Primary Objective:

- To identify the proportion of patients who continue on Major Molecular Response after discontinuing treatment with TKI.

Secondary objectives:

• To characterize the immunological status of patients with CML at the time of interruption and then at 3 and 12 months after the interruption.

Tertiary objective: To evaluate the pharmacoeconomic impact of interrupting the treatment.

Inclusion criteria:

1. Signed Informed consent.
2. Patients with a diagnosis of CML BCR-ABL positive in CP treated with approved TKI (Imatinib, Nilotinib or Dasatinib) in 1st line or in 2nd line due to intolerance to the 1st line or in 2nd line due to the lack of deep MR with 1st line TKI, which never presented criteria for treatment failure.
3. Age ≥ 18 years
4. ≥ 4 years of treatment with imatinib, nilotinib or dasatinib.
5. Achievement of MR 4.5 in a standardized laboratory (BCR-ABL1 IS ≤ 0.0032%).
6. Evidence of MR 4.5 sustained for ≥ 2 years, as documented in at least 4 tests performed at least 3 months apart.
7. Evidence of typical quantifiable BCR-ABL1 transcript (b3a2 [e14a2] and / or b2a2 [e13a2], typical isoforms of p210).

Exclusion criteria:

1. Patients who previously discontinued TKI and demonstrated recurrence of the disease.
2. Patients with failure to any TKI at any time.
3. Patients who presented accelerated phase or CML in blast crisis at any time.
4. Patients with atypical transcript not quantifiable by RT qPCR
5. BCR-ABL mutation detected at any time during the course of the resistant disease