Spirit 2: An NCRI Randomised Study Comparing Dasatinib with Imatinib in Patients with Newly Diagnosed CML

Objective. SPIRIT 2 is the largest phase 3 prospective randomized open-label trial comparing imatinib 400mg with dasatinib 100mg daily: this is the first presentation of data comparing the two arms.

Methods. 814 patients were recruited at 144 hospitals between August 2008 and March 2013. 812 started study medication (406 in each arm). The primary endpoint is event-free survival at 5 years. A key secondary endpoint is the rate of achievement of a BCR-ABL/ABL ratio of <0.1%^IS (major molecular response (MMR), 3 log reduction or MR³).

Results. Discontinuations. With a median follow up of 34 months a total of 289/812 (35.6%) patients have discontinued study medication. 118/812 (14.5%) patients have discontinued due to non-haematological toxicity: imatinib 47/406 (11.6%); dasatinib 71/406 (17.5%). 40 patients discontinued due to sub optimal response as assessed by the treating physician: imatinib 37/406 (9.1%); dasatinib 3/406 (0.7%). Side effects. Patients receiving imatinib experienced GI toxicity more often than patients receiving dasatinib; fatigue, rash and headache were more common with dasatinib. A higher rate of grade 3/4 thrombocytopenia was observed in the dasatinib arm: imatinib 17/406 (4.2%); dasatinib 52/406 (12.8%). Pleural effusions occurred in 78/406 (19.2%) patients on dasatinib; 13 of 78 (16.7%) patients required drainage. Arterial cardiovascular events (excluding hypertension) were experienced by 10/812 (1.2%) patients: imatinib 2/406 (0.5%; myocardial infarction (MI) x2); dasatinib 8/406 (2.0%; MI x1; angina/acute coronary syndrome x5; peripheral arterial disease x2). Hypertension was observed in 10/812 (1.2%) patients: imatinib 3/406 (0.7%); dasatinib 7/406 (1.7%). Venous CV events occurred in 7/812 (0.9%) patients: imatinib 3/406 (0.7%); dasatinib 4/406 (1.0%).Efficacy.For both PCR and cytogenetic analyses patients that had discontinued their allocated therapy or that did not have a 12 month sample were analysed as not having achieved MR³/CCR. The MR³ (PCR <0.1% ^IS) rate at 12 months in all treated patients is significantly different (p<0.001) between the two treatment arms: imatinib 173/406 (42.6%); dasatinib 236/406 (58.1%). The MR³ rate at 12 months in patients treated with dasatinib is 51/78 (65.4%) in those with a pleural effusion and 185/328 (56.4%) in those without (p=0.148, NS).The complete cytogenetic response (CCR) rate at 12 months is: imatinib 163/406 (40.1%); dasatinib 207/406 (51.0%). The difference between the two treatment arms is statistically significant (p=0.002) but caution is required in interpreting these data as there were missing analyses in 367 of 812 (45.2%) patients: imatinib 191 of 406 (47.0%), dasatinib 176 of 406 (43.3%). The difference in major cytogenetic response (MCR) rate between the two treatment arms at 12 months is not statistically significant: imatinib 200/406 (49.3%); dasatinib 218/406 (53.7%), p=0.206.Disease progression and deaths. 16 patients have progressed to either accelerated phase or blast crisis and 13 of those progressions were within the first year. Accelerated phase: imatinib 3/406 (0.7%); dasatinib 2/406 (0.5%). Blast crisis: imatinib 7/406 (1.7%); dasatinib 4/406 (1.0%).

Conclusions. Dasatinib-treated patients have a higher rate of molecular response at 1 year but, with a median of 34 months follow up, there is no significant difference in rates of disease progression or overall survival. More patients abandoned imatinib than dasatinib due to investigator concerns about sub optimal responses. Further follow up is required to evaluate whether there will be differences in event free survival at five years.