Imatinib (IM) can be safely discontinued in patients with chronic myeloid leukemia (CML) with sustained complete molecular remission. Previous publications from France and Australia have shown that overall 40% maintain MMR or MR5 for up to 5 years after IM is stopped. We report single US center experience with tyrosine kinase inhibitor (TKI) discontinuation. Between 06/2010 and 7/2015, 22 patients with CML in chronic (CP, n=19), accelerated (AP, n=2) and lymphoid blast phase (LBP, n=1) discontinued IM (n=17), dasatinib (DAS, n=3) or bosutinib (BOS, n=2), and were monitored by qPCR for BCR-ABL1 monthly for the first 3 months, quarterly for the following 2 years and then bi-annually. TKI was restarted in case of confirmed loss of MMR on a repeat qPCR. Reason for TKI discontinuation was predominantly driven by patients' request and TKI intolerance. Median age was 66 (range, 21-84). The 3 who discontinued DAS had IM-resistant (loss of CCyR; n=1), IM-intolerant CP (n=1), or received DAS as first-line agent (n=1). BOS was discontinued for IM-intolerant CP (n=1), or while in CR2 in a patient with LBP that transformed from IM resistant CP and relapsed following chemotherapy (HCVAD). Median duration of TKI therapy pre-discontinuation for the entire cohort was 89 months (range, 26-106). Three patients are not evaluable due to short follow-up (TKI stopped between 5/2015 and 7/2015).
With a median follow-up of 40 months (range, 8-60), 7 (41%, 6 CP and 1 AP), all previously on IM lost MMR a median of 3 months (range, 3-24) after TKI was stopped and restarted IM. Loss of CHR occurred 13 months after loss of MMR in 1 patient who elected not to restart IM at the time MMR was lost, due to complications from cardiac transplant rejection. All 7 achieved MMR following restart of IM. Median duration of TKI therapy pre-discontinuation for these 7 patients was 60 months (range, 48-98). 12 patients (59%, 10 CP, 1 AP, 1 LBP) remain off TKI and have not lost MMR, 8 with continuously undetectable BCR-ABL1; and 4 had 1-2 transient detectable BCR-ABL1 at MR4 levels. Median duration of TKI therapy pre-discontinuation for these 12 patients was 87 months (range, 26-106). Loss of MMR-free survival is depicted in the Figure. We conclude that, similar to previous reports, TKI can be safely discontinued in patients with CML without reappearance of BCR-ABL1 in 50-60%.
Jillella:Seattle Genetics, Inc.: Research Funding. Kota:Leukemia Lymphoma Society: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees.
