Dasatinib (SPRYCEL®) vs Escalated Dose of Imatinib (im) in Patients (pts) with Chronic Phase Chronic Myeloid Leukemia (CP-CML) Resistant to Imatinib: Results of the CA180-017 START-R Randomized Study.

Pts with CML resistant to im have few therapeutic options. A growing body of evidence suggests that treatment outcomes can be improved with increased potency of BCR-ABL inhibition. Escalating the dose of im to 800mg/day (d) can overcome some cases of im-resistance, but tolerability and durability of response are significant issues. Dasatinib (SPRYCEL^®, formerly BMS-354825) is a novel, oral, multi-targeted kinase inhibitor of BCR-ABL, SRC, and other kinases that is approximately 300 times more potent than im in vitro. Dasatinib has been shown to be effective and safe in pts with CML resistant or intolerant to im, leading to recent FDA approval. START-R is an international trial of dasatinib 70mg twice daily (BID) and im 800mg/d in pts with CP-CML resistant to prior im 400–600mg/d. Crossover was allowed upon confirmed progression or intolerance despite dose reduction (grade 3/4 non-hematologic toxicity). Dasatinib dose escalation to 90mg BID was allowed for inadequate response at 12 wks, and dose reduction to 50 or 40mg BID for toxicity. Dose reduction of im to 600mg/d was allowed for patients who had not previously received that dose. Major cytogenetic response (MCyR) rate at 12 weeks was the primary endpoint. From Feb–Nov 2005, 150 pts were randomized (2:1), 101 to dasatinib, 49 to im. MCyR to prior im had been seen in 28% of dasatinib and 29% of im pts. With a minimum follow-up of 10 mo, complete hematologic response (CHR) rate was 92% (93 dasatinib pts) vs 82% (40 im pts), and MCyR rate was 48% dasatinib vs 33% im. Of importance, the primary difference was the complete cytogenetic response (CCyR) rate of 35% (35/101) dasatinib vs 16% (8/49) im, suggesting that dasatinib can achieve deeper responses in this patient population. Of pts with no prior CyR to im, 44% (17/39) achieved a MCyR with dasatinib vs 7% (1/15) with higher dose im. MCyR rates of 40% to dasatinib and 20% to im were achieved in pts with baseline im-resistant BCR-ABL mutations, with 47% of dasatinib pts vs 0 im pts with difficult-to-treat P-loop mutations achieving a MCyR. Pts with no prior CyR to im were able to achieve MCyR with dasatinib, but dose escalation of im was not effective. 23% dasatinib pts vs 80% im pts had treatment failure (TF, defined as progression, lack of response, crossover for intolerance, or off treatment). Median time to TF was not reached for dasatinib, and was 3.5 mo (95% CI: 3.3-3.8) for im. 61 pts discontinued the initially assigned treatment, of whom 50 (12 dasatinib; 38 im) crossed over after progression, no response, or intolerance. Of 45 post-crossover pts (38 dasatinib; 7 im), 17 (45%) dasatinib pts achieved MCyR, but no (0%) im pts with 800mg/d achieved MCyR after crossover following dasatinib. Grade 3/4 non-hematologic toxicity was minimal in both arms. All grades of superficial edema and fluid retention were more common with im than dasatinib (41% im vs 15% dasatinib; and 43% im vs 28% dasatinib respectively), whereas pleural effusion was 13% (3% grade 3/4) dasatinib vs 0 im. Cytopenia was more frequent and severe with dasatinib. This is the first clinical trial in pts with CML to include both im and dasatinib arms. Based on nearly 1 year of follow-up, dasatinib clearly appears to be more effective in achieving MCyR than high-dose im in pts who fail 400–600mg/d im. An update with molecular response data and detailed mutational analysis will be presented.