Efficacy of Dasatinib in Patients with Chronic-Phase Chronic Myelogenous Leukemia with Resistance or Intolerance to Imatinib: 2-Year Follow-Up Data from START-C (CA180-013).

Dasatinib (SPRYCEL®) is 325-fold more potent than imatinib against BCR-ABL in vitro and binds to BCR-ABL in both the inactive and active, oncogenic conformations. Dasatinib has been shown to be an effective treatment option for patients with imatinib-resistant or -intolerant chronic-phase chronic myelogenous leukemia (CP-CML). Here we report the extended follow-up of START-C, a 75-center, international study of dasatinib in 387 patients with CP-CML with resistance (n=288) or intolerance (n=99) to imatinib. Recruitment took place from February to July 2005. Dasatinib was administered on a 70-mg BID regimen; dose escalation (90 mg BID) or reduction (50 or 40 mg BID) were allowed for lack of response or toxicity, respectively. Median time from diagnosis of CML was 61 mo (range 32–50). Prior therapy included interferon-α in 65% of patients and stem-cell transplantation in 10%; 55% had received prior imatinib doses >600 mg and 53% treatment with imatinib for >3 years. Best response to prior imatinib therapy was complete hematologic response (CHR) in 82%, and complete (CCyR) and partial cytogenetic response (PCyR) in 19% and 18%, respectively. With a median follow-up of 15.2 mo, CHR was attained in 91% of patients (95% CI 87–93%), major cytogenetic response (MCyR) in 59% (95% CI 54–64%) (52% imatinib-resistant, 80% imatinib-intolerant), and CCyR in 49% (40% imatinib-resistant; 75% imatinib-intolerant). For patients with no prior MCyR to imatinib, 42% achieved a MCyR with dasatinib. A MCyR rate of 59% was recorded for patients with baseline BCR-ABL mutations; responses were seen across all mutations with the exception of T315I. MCyRs were durable, with only 7 of the 230 patients who had achieved a MCyR with dasatinib losing this response. Major molecular response rate (ie, a BCR-ABL/ABL ratio of <0.1% according to the international scale by RQ-PCR) at 12 mo was 25%. Progression-free survival at 15 mo was 90% while overall survival was 96%. Dose interruptions were required for 87% of patients and dose reduction for 73%; the average daily dose administered was 101 mg (range 11–171). Reports of grade 3–4 thrombocytopenia and neutropenia were documented for 48% and 49% of patients, respectively. Non-hematologic toxicity consisted primarily of diarrhea (37%), headache (32%), fatigue (31%), and dyspnea (30%). Pleural effusion was experienced by 27% of patients; this was categorised as grade 1–2 in 21% and grade 3–4 in 6%. Dasatinib-induced cytogenetic responses remain durable in patients with CP-CML resistant or intolerant to imatinib. Updated analyses corresponding to a minimum follow-up of 2 years on all patients will be presented.