Treatment Free Remission for Chronic Phase Chronic Myelogenous Leukemia Patients Who Stopped Tyrosine Kinase Inhibitor Therapy Due to Intolerance
Authors: Singh Daulath , Nand Sucha , Mai Hanh 
Published: November 2019

Introduction: Chronic Myelogenous Leukemia (CML) is a myeloproliferative neoplasm that is often diagnosed in adults between the ages of 25-60. The outcome of the chronic phase CML has dramatically changed due to Tyrosine Kinase Inhibitor (TKI) therapy. There are well established guidelines from NCCN and ESMO on stopping TKI for patients achieving prolonged remissions with TKIs. We report clinical outcomes from a single tertiary care center in patients who stopped TKI therapy for reasons other than prolonged remission status.
Methods: We retrospectively reviewed all the CML patients who were treated at our institution in the past 10 years (January 1st,2009 - December 31st,2018). We excluded patients who had accelerated or blast phase CML, atypical CML, patients on non-TKI therapy, and patients who received an allogeneic stem cell transplant.
Results: A total of 117 patients were diagnosed with chronic phase CML at our institution in the past 10 years. Among the 117 patients, 12 of these discontinued TKI therapy. Six patients stopped TKI after achieving prolonged remission with TKI therapy and the remaining patients discontinued due to intolerance to treatment, fear of side effects, and loss of insurance. The median age of the whole cohort is 66 years (range 42-85). Six patients were male and 6 were females. Six patients were diagnosed with CML prior to year 2009 and rest after 2009. Prior to stopping, six patients received only 1 kind of TKI, 2 patients were treated with 2 types of TKIs, 2 patients received 3 types of TKIs, and 2 patients had 4 lines of TKIs (See Table).
Cohort 1: 6 patients who stopped due to prolonged remission, median major molecular remission - MMR4 (BCR-ABL &lt;0.01% IS by RT-PCR testing) prior to stopping TKI is 6 years (range 3-13 years). Of the six, only 1 relapsed (within 1 month of stopping) and was initiated back on the same TKI (imatinib). The relapsed patient has not achieved MMR4 level remission to date. Median treatment free remission for this cohort is 13 months (range 1-24 months).
Cohort 2: Of those 6 patients who stopped TKI for other reasons: 4 stopped due to side effects/intolerance, 1 stopped due to fear of side effects after FDA label was updated, and 1 patient discontinued due to a loss of insurance. Median duration of MMR4 prior to stopping is 4 years (range 1-11 years). 5 of these 6 patients relapsed in the median time of 6 months (range 3-16 months). Of these 5, 4 were started back on the TKI therapy (three on the same TKI and one on a different TKI). Median treatment free remission for this cohort is 4 months (range 2-16 months).
Conclusion: In this small cohort from a single institution's experience, CML patients who discontinued TKI therapy after achieving MMR4 for reasons other than prolonged remission have experienced poor outcomes including a higher rate of relapse and a shorter treatment free remission. We need studies with larger samples sizes and longer follow up to assess outcomes in patients stopping TKI therapy for various reasons.

Disclosures
No relevant conflicts of interest to declare.