Treatment-free remission (TFR) in patients (pts) with chronic myeloid leukemia in chronic phase (CML-CP) treated with second-line nilotinib (NIL): First results from the ENESTop study.

7054Background: The ENESTop (NCT01698905) study explores the discontinuation of NIL therapy in pts who achieved sustained MR4.5 (BCR-ABL1IS≤ 0.0032%) after switching from imatinib (IM) to NIL. Methods: The single-arm phase 2 study enrolled pts with CML-CP treated with tyrosine kinase inhibitor (TKI) for ≥ 3 y (including IM for > 4 wk followed by NIL for ≥ 2 y) and achieved MR4.5 on NIL. On study, pts continued NIL for 1 y (consolidation phase [CONS]). After 1 y, pts without confirmed loss of MR4.5 (consecutive BCR-ABL1IS > 0.0032%), were eligible to stop NIL (TFR). RQ-PCR was monitored every 12 wk in CONS and every 4 wk during first 48 wk of TFR. Upon confirmed loss of MR4 (consecutive BCR-ABL1IS > 0.01%) or loss of MMR (BCR-ABL1IS> 0.1%), NIL was re-initiated (ReRx). Primary endpoint was the proportion of pts with successful TFR (neither loss of MMR nor confirmed loss of MR4 by 48 wk of TFR) after a ≥ 48 wk follow up (data cutoff, 26 Nov 2015). Results: Of the 163 pts in CONS, 126 entered TFR (median dur...