The first purpose of this study is to evaluate the persistence of the complete molecular remission in patients with Chronic Myeloid Leukemia after stopping imatinib treatment (determine by Reverse Transcription real-time Polymerase Chain Reaction (RT-PCR) negative for bcr-abl transcripts). The second purpose is to determine clinicals and biologicals factors associated with the persistent complete molecular remission.

Principal Objective : To evaluate the complete molecular remission persistence after stopping imatinib during six months as measured by RT-PCR negative for bcr-abl transcripts in patients with Chronic Myeloid Leukemia .

Secondary Objective :

• To determine clinicals factors associated with complete molecular remission before and after stopping imatinib in patients with Chronic Myeloid Leukemia.
• To determine the biologics factors (immunologic and molecular) associated with complete molecular remission before and after stopping imatinib in patients with Chronic Myeloid Leukaemia.
• To determine the molecular relapse level after more than six month of persistent complete molecular remission without imatinib.
• To determine the complete molecular remission length.
• To evaluate medical and economical impact of stopping imatinib treatment.

Study design : multicentric trial

Inclusion Criteria:

• Patients must have reached their 18th birthday
• Women of childbearing potential must agree to use effective methods of contraception
• Patients must be affiliated to a social security regime
• Patients must have received imatinib therapy for at least 36 months.
• Patients must be in complete molecular remission during at least two consecutive years with at least five RT-PCR negative measures for bcr-abl transcripts.
• Patients must be HIV, HCV and HBV negatives
• Patients who have molecular follow-up realized in accordance with international recommendations
• All patients must be informed of the investigational nature of this study and must sign and give written informed consent.

Exclusion Criteria:

• Patients who are protected by the law. Patients who are unable to give their consent to participate to the study.
• Patients who have pathologies or treatments that are able to enhance the potential relapse risk after stopping imatinib. Patients who have pathologies or treatments which able to interfere with immunologic study (excepted IFN α):

Corticosteroids or other immuno suppressors Other concomitant malign pathology treated by chemotherapy or radiotherapy Previous or programmed Haematopoietic Stem Cell allogreffe