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The phase 3 EPIC trial, a comparison of tyrosine kinase inhibitors (TKIs), has left some questions unanswered.
The trial did not determine whether the third-generation TKI ponatinib is more effective than the first-generation TKI imatinib for patients with previously untreated chronic myeloid leukemia (CML).
The study was terminated early due to safety concerns associated with ponatinib, so the primary endpoint could only be analyzed in a small number of patients.
Results in these patients showed no significant difference in that endpoint—major molecular response (MMR) at 12 months—between the imatinib and ponatinib arms.
Results in the entire study cohort suggested that, overall, ponatinib was more toxic than imatinib. In particular, ponatinib produced more arterial occlusive events.
However, the trial’s investigators have questioned whether reducing the dose of ponatinib might change that.
Jeffrey H. Lipton, MD, of Princess Margaret Cancer Centre in Toronto, Ontario, Canada, and his colleagues reported results from the EPIC trial in The Lancet Oncology. The trial was supported by Ariad Pharmaceuticals.
Problems with ponatinib
Ponatinib was approved by the US Food and Drug Administration (FDA) in December 2012 to treat adults with CML or Philadelphia chromosome-positive acute lymphoblastic leukemia that is resistant to or intolerant of other TKIs.
In October 2013, follow-up results from the phase 2 PACE trial suggested ponatinib can increase a patient’s risk of arterial and venous thrombotic events. So all trials of the drug were placed on partial clinical hold, with the exception of the EPIC trial, which was terminated.
That November, the FDA suspended sales and marketing of ponatinib, pending results of a safety evaluation. In December, the agency decided ponatinib could return to the market if new safety measures were implemented. In January 2014, ponatinib was put back on the market in the US.
EPIC trial
The trial enrolled 307 patients with newly diagnosed, chronic-phase CML. Patients were randomized to receive ponatinib at 45 mg (n=155) or imatinib at 400 mg (n=152) once daily until progression, unacceptable toxicity, or other criteria for withdrawal were met.
The median age was 55 (range, 18-89) in the ponatinib arm and 52 (range, 18-86) in the imatinib arm. Most patients were male—63% and 61%, respectively—and most had an ECOG performance status of 0—75% and 78%, respectively.
Patients were randomized between August 14, 2012, and October 9, 2013, and the trial was terminated on October 17, 2013.
Because of the early termination, only 10 patients in the ponatinib arm and 13 in the imatinib arm were evaluable for the primary endpoint—MMR at 12 months. Eighty percent (8/10) of the evaluable patients in the ponatinib arm and 38% (5/13) of those in the imatinib arm achieved an MMR at 12 months (P=0.074).
The investigators also evaluated the incidence of MMR at any time in patients with any post-baseline molecular response assessment. This time, the incidence of MMR was significantly higher in the ponatinib arm than the imatinib arm—41% (61/149) and 18% (25/142), respectively (P<0.0001).
All of the patients were evaluable for safety—154 in the ponatinib arm and 152 in the imatinib arm.
Arterial occlusive events occurred in 7% (n=11) of patients in the ponatinib arm and 2% (n=3) in the imatinib arm (P=0.052). These events were considered serious in 6% (n=10) and 1% (n=1), respectively (P=0.010).
Common grade 3/4 adverse events—in the ponatinib and imatinib arms, respectively—were increased lipase (14% vs 2%), thrombocytopenia (12% vs 7%), rash (6% vs 1%), and neutropenia (3% vs 8%).
Serious adverse events that occurred in 3 or more patients in the ponatinib arm were pancreatitis (n=5), atrial fibrillation (n=3), and thrombocytopenia (n=3). There were no serious adverse events that occurred in 3 or more patients in the imatinib arm.
Dr Lipton and his colleagues said the premature termination of the EPIC trial restricts the interpretation of its results, but the available data provide some insight into the activity and safety of ponatinib in previously untreated CML.
The investigators also noted that data from this trial and the clinical development program for ponatinib suggest that lowering doses of the drug could improve its vascular safety profile and, therefore, the benefit-risk balance.
Two ongoing trials (NCT02467270 and NCT02627677) may provide more insight. Both are investigating starting doses of ponatinib at 15 mg or 30 mg.
