Kinetics of Molecular Response with Different Tyrosine Kinase Inhibitors (TKI) Used As Frontline Therapy in Chronic Myeloid Leukemia-Chronic Phase (CML CP),

Abstract Abstract 3784 Background: TKI are standard therapy for patients with CML CP. Imatinib was first established as frontline therapy and more recently dasatinib and nilotinib have shown improved rates and speed of response. Early molecular response has been associated with improved long-term outcome (Blood 2009; 113: 6315), thus the kinetics and rates of molecular response are important predictors of long-term outcome. Aim: To determine the kinetics and rates of molecular response with different TKIs used as initial therapy for patients with CML CP. Methods: We evaluated all pts treated with frontline TKIs (imatinib standard dose or high dose, dasatinib and nilotinib) in consecutive or parallel trials. Cytogenetic and molecular responses were assessed at least every 3 months for the first 12 months, then every 6 months, and were defined using the recommendations of European LeukemiaNet. Molecular responses were defined using international scale. Survival was calculated by the Kaplan-Meier method. Results: Of the 485 pts treated, 73 received imatinib 400mg; 208 imatinib 800mg; 99 dasatinib, and 105 nilotinib. Median age was 48 years (15–86) and median time from diagnosis to TKI therapy was 1 mo (1–13). The median follow-up for each group were 109 months (mo) with imatinib 400, 69 mo with imatinib 800, 30 with dasatinib and 25 mo with nilotinib. Nineteen pts with clonal evolution, but otherwise in CP, were included. Sokal risk score was high in 7%, intermediate in 24% and low in 69%. Cumulative rates of complete cytogenetic response (CCyR) were: imatinib 400mg 87%; imatinib 800mg 91%; dasatinib 96%; and nilotinib 94%. The rate of MMR with imatinib 400mg was 73%, with imatinib 800mg 87%, dasatinib 86%, and nilotinib 88%. Rates of CMR (BCR-ABL/ABL ≤0.0032% IS) were 51%, 71%, 61% and 62%. Median time to achieve MMR and CMR were: imatinib 400mg, 12 mo (3–60) and 18 mo (3–60); imatinib 800mg, 6 mo (3–60) and 9 mo (3–60); dasatinib, 6 mo (3–36) and 12 mo (3–54), and nilotinib 6 mo (3–48) and 6 mo (3–42). The median transcript levels at 3, 6, 12, 18, 24 and 36 mo by treatment arm are shown in table 1 . The rates of MMR and CMR at 36 mo for imatinib 400mg were 58% and 34%. Corresponding rates for imatinib 800mg were 87% and 59%; for dasatinib 87% and 54%; and for nilotinib 90% and 63%. We then assessed the probability of achieving MMR and CMR at 12 mo according to the BCR-ABL/ABL levels at earlier timepoints. Two of 9 (22%) evaluable pts with transcript level >10 at 3 mo achieved a MMR at 12 mo but none achieved a CMR. In contrast, 31/52 (60%) evaluable pts with transcript level >1–10 at 3 mo, achieved a MMR at 12 mo and 4 (8%) achieved a CMR. Similarly, pts with level >0.1–1 at 3 mo, 72/129 (56%) evaluable pts achieved a MMR and 29 pts (22%) a CMR at 12 months. For each individual TKI, a similar trend was noted where a higher transcript level (>10; >1–10; >0.1–1) at 3 mo was associated with a decline in achieving a MMR and CMR at 12 mo (MMR- imatinib 400mg: 0%; 50%; 67%, imatinib 800mg: 0%; 62%; 80%, dasatinib: 33%; 67%; 71%, nilotinib: 100%; 50%, 88%, CMR-imatinib 400mg: 0%, imatinib 800mg: 0%; 8%; 10%, dasatinib:0%; 17%; 29%, nilotinib: 0%; 0%; 32%). The probability of transformation to AP/BP by transcript levels at 3 mo (>10; >1–10; >0.1–1, ≤0.1) was 0%, 3%, 2% and 1% for the overall population, with similar trends for the different therapies. Table 1 . Median transcript levels by treatment arm 3 mo 6 mo 12 mo 18 mo 24 mo 36 mo Imatinib 400 0.2005 0.3360 0.0399 0.0084 0.0030 0.0079 Imatinib 800 0.1810 0.0183 0.0084 0.0049 0.0044 0.0027 Dasatinib 0.2150 0.0336 0.0140 0.0070 0.0032 0.0032 Nilotinib 0.1610 0.0210 0.0105 0.0032 0.0032 0.0032 Conclusion: New TKI provide a faster improvement in molecular response among pts with CML CP receiving TKI as initial therapy. Early responses are equally predictive of long-term outcome across all treatment options. Disclosures: Kantarjian: Novartis: Consultancy, Research Funding; BMS: Research Funding; Pfizer: Research Funding. Ravandi: Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria. Cortes: BMS: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; ChemGenex: ChemGenex is now Cephalon, Inc., Consultancy, Research Funding; Deciphera: Research Funding.