Outcomes of Chronic Phase Chronic Myeloid Leukemia Patients Following Tyrosine Kinase Inhibitors Dose-Reductions

Introduction: Tyrosine kinase inhibitors (TKI) are overall well tolerated in chronic myeloid leukemia (CML) s, but more than 30% require dose reduction or change to another TKIs due to intolerance. Impact of TKI dose-reduction on outcomes in a "real world" setting is unknown, thus, we evaluated the characteristics and outcomes of chronic phase (CP)-CML patients who received doses of TKI lower than the label/FDA recommendation.

Method: CP-CML with at least 12 months of follow-up, with ^ISBCR/ABL1 available after dose reduction were selected. Last TKI was defined as TKI which were taken at the last follow up visit or before disease progression to accelerated (AP) or blast phase (BP). FDA approved doses of imatinib (IM), dasatinib (DAS), nilotinib (NIL), bosutinib (BOS), and ponatinib (PON) were 400mg, 100mg, 600mg (300mg BID), 500mg, and 45mg, respectively .

Results: Between January 2005 and April 2016, 173 CP-CML patients, started IM (75%), DAS (18%) NIL (5%) and PON, BOS on clinical trial in 2%. Overall Fifty-eight (33.5%) patients had TKI dose reduction. IM (n=15) dose was reduced to 75% (range, 25-75), DAS (n=15) to 50% (range, 20-80), NIL (n=15) to 50% (range, 13-67), BOS (n=15) to 80% (range, 40-80) and PON (n=15) to 33% (range, 33-67). Median age for patients that received dose-reduced TKI was 55 (range, 18-88), and 27% received > 3 prior TKIs. With a median follow up of 53.6 (range 13.4-183.7) months, only 1 progressed to AP, and none to BP. Overall 60% achieved MMR. Among 35 patients who achieved MMR before dose reduction, MMR was maintained in 25 (71.4%) for a median of 17.2 (2-97.9) months from dose-reduction. CMR was achieved in patients on a maintenance dose of IM, 100mg QD (n=8); DAS, 20mg QD (n=4); NIL 300mg QD (n=3) and BOS, 200mg QD (n=3).

Conclusion: Similar to data reported from clinical trials, TKI dose reduction appears to be safe and associated with high response rates. This data confirms that the minimal effective dose for each TKI remains to be defined.