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Panitumumab increased progression-free survival in patients with colorectal cancer
Patients receiving the fully human antibody did not exhibit hypersensitivity reactions typical of humanized antibodies.
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WASHINGTON — A randomized, phase-3 study showed that panitumumab (Amgen) improved progression-free survival in patients with metastatic colorectal cancer who failed standard chemotherapy.
“We are encouraged by these results, particularly that panitumumab was well tolerated in patients with metastatic colorectal cancer, with very few major adverse reactions,” said Marc Peeters, MD, PhD, coordinator of the digestive oncology unit at Ghent University Hospital in Belgium. Peeters presented his findings here at the 97th Annual Meeting of the American Association for Cancer Research.
Panitumumab delivery
The study compared 231 patients who received 6 mg/kg of panitumumab every two weeks and the best supportive care with 232 patients who received only the best supportive care. Eligible patients had metastatic colorectal cancer with documented progression following fluoropyrimidine, irinotecan (Camptosar, Pfizer) and oxaliplatin (Eloxatin, Sanofi-Aventis) treatment.
Patients in the panitumumab arm showed a 46% decrease in the rate of tumor progression or death compared with those in the control arm (HR=0.54). By week eight, there was a higher percentage of patients alive without progression in the panitumumab arm than in the best supportive care arm (49% vs. 30%, respectively). This difference in the percentage of patients alive favoring panitumumab continued through week 32, according to researchers.
At week 24, about 18% of patients receiving panitumumab were alive and progression-free vs. 5% of those receiving the best supportive care. At week 32, 10% of patients receiving panitumumab were alive compared with 4% of patients in the control arm.
Panitumumab also improved disease control. In responders, the median duration of response was 17 weeks. Extended follow-up also revealed that even after 32 weeks, a larger percentage of patients in the panitumumab arm were alive without progression than in the group assigned to the best supportive care alone.
“The distinguishing feature based on the activity seen in this trial, is that [panitumumab] improved progression-free survival,” said James L. Abbruzzese, MD, chairman of gastrointestinal medical oncology at the University of Texas MD Anderson Cancer Center in Houston, “particularly in the early phase of the trial where patients on [the best supportive care] were either failing or dying very quickly and the effect of panitumumab was obvious and fairly impressive.”
Human protein sequence
More patients in the panitumumab arm developed skin-related toxicities (rash) vs. patients in the control arm (90% vs. 9%, respectively). Other adverse events were less frequent. In the panitumumab arm, 9% more patients experienced fatigue, 6% more patients experienced abdominal pain, 7% more patients experienced nausea and 10% more patients experienced diarrhea than in the control arm. No patients had grade-3 and -4 infusion-related reactions. One patient discontinued panitumumab due to a grade-2 hypersensitivity reaction, researchers said.
Panitumumab is a fully human monoclonal antibody. Derived from human protein sequences, such an antibody is less likely to cause adverse events like hypersensitivity reactions.
“We expected there to be fewer hypersensitivity reactions and in fact that’s what we’ve seen,” Abbruzzese said. “This result will be very important in Europe. These patients did not in general have access to, or treatment with, any of the available antibodies like bevacizumab (Avastin, Genentech) or cetuximab (Erbitux, ImClone). So potentially in Europe, approval of panitumumab offers a major new option to patients refractory to chemotherapy. In the Unites States the issues are a little more complex because of the issues of second- and third-line treatment with cetuximab.” – by Mark Palacio
For more information:
- Peeters M, Van Cutsem E, Siena S, et al. A phase 3, multicenter, randomized controlled trial (RCT) of panitumumab plus best supportive care (BSC) vs. BSC alone in patients (pts) with metastatic colorectal cancer (mCRC). Abstract CP-1. Presented at: 97th Annual Meeting of the American Association for Cancer Research; April 1-5, 2006; Washington.