Nilotinib Lowers the Incidence of BCR-ABL Mutations and Improves the Molecular Response Kinetics Compared with Imatinib in Patients (Pts) with Newly Diagnosed Chronic Myeloid Leukemia (CML).

In the ENESTnd (Evaluating Nilotinib Efficacy and Safety in Clinical Trials–Newly Diagnosed Pts) trial, nilotinib demonstrated superior efficacy vs imatinib in newly diagnosed pts. Here, we examined the kinetics of molecular response and BCR-ABL mutation status in pts from ENESTnd.

Pts with CML-CP were randomized to receive nilotinib 300 mg twice daily (bid) (n = 282), nilotinib 400 mg bid (n = 281), or imatinib 400 mg once daily (qd) (n = 283). BCR-ABL transcripts were quantified at baseline (BL) and every 3 months (mos); MMR was defined as ≤ 0.1% BCR-ABL on the International Scale (IS). Mutational testing of BCR-ABL was performed by direct sequencing at BL and at the occurrence of: (i) 5-fold increase in PCR levels, (ii) failure to achieve MMR at 12 mos, (iii) loss of MMR (≥ 0.1% BCR-ABL^IS confirmed by a subsequent sample in association with a ≥ 5-fold rise in BCR-ABL from the lowest value achieved on study treatment), and (iv) end of treatment. Median follow-up was 18 mos.

During therapy, a more rapid decline in BCR-ABL levels was demonstrated in the nilotinib arms vs imatinib (Table). The median BCR-ABL levels for pts on nilotinib at 6 mos (both arms) were similar to those on imatinib at 18 mos. The median time to MMR among responders was also shorter on nilotinib (6, 8, and 10 mos in the nilotinib 300 mg bid, 400 mg bid, and imatinib arms, respectively). Loss of MMR occurred in 14 (2%) pts (6 [2%], 5 [2%], and 3 [1%] in the nilotinib 300 mg bid, 400 mg bid, and imatinib arms). Of the 14, none progressed to accelerated phase/blast crisis (AP/BC); only 1 of these pts showed a BCR-ABL mutation (M244V) in the imatinib arm, and 1 pt in the nilotinib 300 mg bid arm lost CCyR. Overall, 9 of 14 (64%) pts, including 8 of 11 on nilotinib, regained MMR within 6 mos on their assigned therapy. In 3 of these 9 pts who regained MMR, loss of MMR was concurrent with dose reduction, and MMR was regained at the time of dose re-escalation. Poor compliance may have contributed to fluctuations in BCR-ABL levels in some pts. At BL, no BCR-ABL mutations were found; 60 pts had polymorphisms which were equally distributed among the 3 arms. Mutational testing was triggered on therapy in 164, 171, and 199 pts in the nilotinib 300 mg bid, 400 mg bid, and imatinib arms, respectively, most commonly due to lack of MMR at 12 mos. Approximately twice as many BCR-ABL mutations (16 [6%]) developed in the imatinib arm vs nilotinib arms (8 [3%] and 5 [2%] for 300 mg bid and 400 mg bid), and most of these were detected within the first 12 mos. The majority of mutations in the nilotinib arms were less sensitive (Y253H, E255K, F359V) or resistant (T315I) to nilotinib, while both nilotinib-sensitive and insensitive mutations were detected in the imatinib arm (Table). The T315I mutation emerged in 5 pts: 2 on nilotinib 300 mg bid, 1 on nilotinib 400 mg bid, and 2 on imatinib; two of these 5 pts discontinued therapy. Overall, 6 of 16 pts with mutations on imatinib progressed to AP/BC vs only 1 of 13 pts on nilotinib (Table). Minimum 24 month follow-up data for all pts will be presented.

Pts treated with nilotinib had faster and deeper molecular responses compared with imatinib. The incidence of new mutations was highest for imatinib, and most pts with mutations on nilotinib have not progressed with 18 mos of median follow-up. Loss of MMR was infrequent and was regained in the majority of cases without a change in therapy, and was not typically associated with subsequent treatment failure or the emergence of new mutations. Therefore, loss of MMR may not be an indicator for adjusting therapy, although close monitoring for further loss of response is warranted and mutation testing may be considered.

Hochhaus:Novartis: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding. Saglio:Novartis: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria. Larson:Novartis: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding. Kim:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Flinn:Novartis: Research Funding. Goh:Novartis: Honoraria, Research Funding; Janssen Ciliag: Honoraria, Research Funding; Celgene: Honoraria; Bristol Myers Squibb: Honoraria. Dorlhiac-Llacer:Novartis: Honoraria, Research Funding; Bristol Myers Squibb: Research Funding; Wyeth: Research Funding. Porkka:Novartis: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding. Kurokawa:Novartis: Consultancy; Shionogi & Co., Ltd.: Consultancy. Shou:Novartis: Employment. Gallagher:Novartis Pharma AG: Employment, Equity Ownership. Haque:Novartis: Employment. Kantarjian:Novartis: Consultancy, Research Funding; Bristol Myers Squibb: Research Funding; Pfizer: Research Funding. Hughes:Novartis: Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Research Funding; Ariad: Honoraria.