The Life After Stopping Tyrosine Kinase Inhibitors Study (The LAST Study)

Inclusion Criteria:

1. Age 18 or older at time of study entry
2. Willing and able to give informed consent
3. Diagnosed with CML in chronic phase and have either the b3a2 (e14a2) or b2a2 (e13a2) variants that give rise to the p210 BCR-ABL protein
4. Currently taking imatinib, dasatinib, nilotinib or bosutinib
5. Patient has been on TKI therapy for at least 3 years
6. Documented BCR-ABL \<0.01% (\>MR4 i.e. \>4 log reduction) or undetectable BCR-ABL by PCR for at least 2 years according to the patient's local lab
7. Documented BCR-ABL \<0.01% (\>MR4 i.e. \>4 log reduction) or undetectable BCR-ABL at least 3 times prior to screening according to the patient's local lab
8. Two (2) Screening PCRs have been completed and both results are \< 0.01% (\>MR4 i.e \> 4 log reduction) by central lab
9. Has been on any number of TKIs, but has not been resistant to any TKI (changes made for intolerance are allowed)
10. Patient has been compliant with therapy per treating physician

Exclusion Criteria:

1. Prior hematopoietic stem cell transplantation
2. Poor compliance with taking TKI
3. Unable to comply with lab appointments schedule and PRO assessments
4. Life expectancy less than 36 months
5. Patients who have been resistant to previous TKI therapy are not eligible
6. Pregnant or lactating women