Background: The 12-mo results of ENESTcmr demonstrated that switching pts on IM with sustained BCR-ABL positivity to NIL leads to faster, deeper molecular responses (MRs)vs remaining on IM. These deeper molecular responses (MR^4.5 [BCR-ABL ≤ 0.0032%^IS] or greater) are a prerequisite to enter most treatment-free remission studies. Here, we report 24-mo f/u of ENESTcmr. Methods: Philadelphia chromosome–positive CML-CP pts (N = 207) who achieved a complete cytogenetic response, but had detectable BCR-ABL transcripts after ≥ 2 y on IM, were randomized to receive NIL 400 mg twice daily (BID; n = 104) or continue their IM dose (400/600 mg once daily [QD]; n = 103). Results: By 24 mo, significantly more pts achieved confirmed undetectable BCR-ABL (by RQ-PCR with ≥ 4.5 log sensitivity in 2 consecutive samples) with a switch to NIL vs continuing IM (22.1% vs 8.7%; P = .0087). The increase in the rate of undetectable BCR-ABL from mo 12 to 24 was higher for pts on NIL vs IM (9.6 vs 2.9 percentage points). In pts without MR^4.5 at baseline (BL), MR^4.5 was achieved by 24 mo in 42.9% vs 20.8% of pts (NIL vs IM; P = .0006). In pts without major molecular response (MMR; ≤ 0.1%^IS) at BL, MR^4.5 was achieved by 24 mo in 29.2% vs 3.6% of pts (P = .016). No progressions to accelerated phase/blast crisis or deaths occurred on study since the 12-mo f/u. Event-free survival at 24 mo was 96.6% vs 92.8% in the NIL and IM arms, respectively. Discontinuations due to adverse events occurred in 11.5% and 2.9% of pts in the NIL and IM arms. The NIL safety profile was consistent with prior switch studies. Conclusions: By 24 mo, significantly more pts achieved deeper responses (MR^4.5and undetectable BCR-ABL) with switch to NIL vs remaining on IM, and the difference between arms in these endpoints increased between 12 and 24 mo. Clinical trial information: NCT00760877.