Stopping study in chronic myeloid leukemia: Defining a new paradigm for Ontario CML1

e19069 Background: The National Comprehensive Cancer Network (NCCN) guidelines state that in order to safely stop tyrosine kinase inhibitor (TKI) therapy in chronic myeloid leukemia (CML) patients, we need access to reliable polymerase chain reaction (PCR) tests on a monthly basis (4 weeks). However, Ontario, Canada can only provide a 6-week turnaround reliably. Therefore, we aimed to test a new paradigm for safely stopping TKI treatment by monitoring molecular response every 6 weeks for 6 months instead of the recommended 4-week intervals. Methods: A prospective pilot cohort study was conducted to assess the outcome of cessation of TKI treatment in chronic-phase CML patients. Eligibility criteria includes obtaining MMR4 (4-log reduction) for 2 years and had to have been on TKI therapy for 5 years. Patients' PCR for BCR-ABL, a driver of CML, was tested every 6 weeks for 30 weeks to ensure ongoing major molecular response (MMR). The primary endpoint was successful maintenance of MMR3 (3-log reduction) or greater at 36 weeks. Secondary endpoints include incidence of withdrawal syndrome, psychological effects, and quality of life (QoL) as per the EORTC Global Quality of Life scoring system were assessed during each visit every 6 weeks for 30 weeks. The secondary endpoint was assessing whether MMR was regained once lost. Results: 18 consenting patients were enrolled, 2 were censored from data analysis as additional time is required to assess whether they regained deep molecular response after stopping, 1 patient was deemed too early to analyze. 12 of the 17 enrolled participants were able to successfully stop TKI therapy and remain in remission at 30 weeks, yielding a 71% success rate. 5 patients had relapsed and 3 successfully regained MR 3.0 with resumption of TKI therapy. Conclusions: The findings demonstrated in a small pilot study that testing at 6-week intervals is safe and effective. Most Ontario CML patients treated in large community centers and have not stopped TKI therapy based on the NCNN guidelines that recommend a 4-week testing turnaround. We plan to expand this study to other sites in Ontario and if successful, this new paradigm may enable more CML patients to stop TKI therapy in a safe manner leading to significant financial and clinical impact. Data will be updated at the time of the conference. By determining that Q6 weekly is a safe paradigm, there is potential for increased comfort in patients unable to maintain Q4 weekly testing for various reasons such as compliance or patients in rural settings. Clinical trial information: OCT1250 , CML1 .