Amgen announced final results from a pivotal Phase III trial showing that Vectibix, a fully human monoclonal antibody directed against the epidermal growth factor receptor (EGFr), prolonged progression-free survival (PFS) compared with best supportive care in metastatic colorectal cancer patients who had failed fluoropyrimidine-, irinotecan- and oxaliplatin-containing chemotherapy regimens. The results were published in the May issue of the Journal of Clinical Oncology.
The FDA’s approval of Vectibix (panitumumab) last September was based on the results from this multinational, open-label, randomized study of 463 patients. Patients were randomized to receive 6 mg/kg of Vectibix plus standard care every two weeks or standard care alone until disease progression or unacceptable toxicity. Patients receiving best supportive care and determined to have disease progression were eligible to cross over to a separate study and receive Vectibix.
The primary endpoint of this study was an improvement in PFS. Co-secondary study endpoints were best objective response by blinded central review and overall survival time. The effectiveness of Vectibix for the treatment of EGFr-expressing, metastatic colorectal cancer is based on PFS.
As seen in previous analyses of these data, the Vectibix group showed a statistically significant improvement in PFS versus those who received standard alone, yielding a 46 percent decrease in the relative progression rate. The mean PFS was 96 versus 60 days.
A blinded central review showed that 10 percent of patients in the Vectibix group had an objective response, while no patients in the standard care group demonstrated an objective response. Median time to response was 7.9 weeks, and median duration of response was 17 weeks.
In the primary analysis of overall survival, there was no significant difference between the groups. The median follow-up time was 72 weeks for all patients.