Amgen announced detailed results from the phase-3 '181' trial evaluating Vectibix (panitumumab) in combination with Folfiri (an irinotecan based chemotherapy), as a second-line treatment for metastatic colorectal cancer (mCRC). In this trial, Vectibix significantly improved progression-free survival (PFS) in patients with KRAS wild-type mCRC. These results were presented at the 2009 ECCO 15 - ESMO 34 European Multidisciplinary Congress in Berlin, Germany (Abstract Number 14LBA).

The addition of Vectibix to Folfiri significantly improved median PFS (co-primary endpoint) by two months (5.9 versus 3.9 months for patients treated with Folfiri alone, hazard ratio 0.73, p=0.004) in patients with KRAS wild-type mCRC. Although numerically greater (14.5 months versus 12.5 months; hazard ratio 0.85), the improvement in median overall survival (co-primary endpoint) in the Vectibix arm did not achieve statistical significance (p=0.115) in the same patient population.

Further, the addition of Vectibix to Folfiri resulted in greater than a three-fold improvement (35 per cent versus 10 per cent) in response rate in the KRAS wild-type patient population as measured by a blinded central review.

"This study showed that Vectibix can be safely administered in combination with Folfiri chemotherapy. Vectibix delayed disease progression by more than half compared to Folfiri alone in patients with previously treated KRAS wild-type colorectal cancer," said Marc Peeters, coordinator of Digestive Oncology Unit, University Hospital Ghent and the study's principal investigator. "Further, the response rate seen in this trial is among the highest ever reported in the second-line metastatic CRC setting."

In general, adverse events rates were comparable across arms with the exception of known toxicities associated with anti-epidermal growth factor receptor (EGFR) therapy such as rash, diarrhoea, and hypomagnesemia. Vectibix-related grade 3/4 infusion reactions were reported in less than one percent of patients.

There were no differences in progression-free survival, overall survival and response rates among patients with mutated KRAS who received Vectibix.

Originally designed to compare the treatment effect in the overall population, the study was amended to analyze outcomes with respect to the presence or absence of activating mutations in KRAS in the tumour itself. Tumour KRAS status was ascertained in 91 percent of the 1,186 patients enrolled in this trial, the highest number ever reported for a second-line trial.

"These high quality prospectively defined analyses prove the clinical utility of KRAS as a predictive biomarker in metastatic colorectal cancer patients," added Peeters.

Vectibix is the first fully human anti-EGFR antibody approved by the US Food and Drug Administration (FDA) for the treatment of mCRC. Vectibix was approved in the United States in September 2006 as a monotherapy for the treatment of patients with EGFR expressing mCRC after disease progression on or following fluoropyrimidine-, oxaliplatin-, and irinotecan-containing chemotherapy regimens.