Amgen shares have taken a battering from the news that the firm has discontinued a late-stage trial of Vectibix which was designed to prove the drug’s efficacy as part of a potential first-line treatment for patients with colorectal cancer.

The Phase IIIb 1,054-patient trial was evaluating the addition of Vectibix (panitumumab) to oxaliplatin- and irinotecan-based chemotherapy and Avastin (bevacizumab) for the treatment of first-line metastatic colorectal cancer and after an interim analysis, conducted after 231 events (death or disease progression), it was revealed that the results were worse in the Vectibix arm than the comparison cohort, which received Avastin and chemotherapy by themselves. Those patients in the control arm experienced a statistically significant better result in progression-free survival.

Roger Perlmutter, executive vice president of R&D at Amgen, said that “unfortunately, it appears that adding Vectibix to Avastin, when used in combination with oxaliplatin- or irinotecan-based chemotherapy, increased toxicity, without improving efficacy," and the company has notified the US Food and Drug Administration and study investigators that patients who are still receiving treatment in the study, called PACCE, should discontinue Vectibix treatment.

Vectibix, an epidermal growth factor receptor inhibitor, was approved by the FDA last September as a second- and third-line monotherapy for colorectal cancer and Amgen was hoping to expand the use of the drug into the adjuvant setting, which could place it head-to-head with ImClone System’s Erbitux (cetuximab), which is approved for use as a first-line treatment in combination with chemotherapy.

Unsurprisingly, the news of the premature end to the PACCE trial led to a rise in ImClone shares and a number of brokers reduced their estimates on Amgen. Analysts at RBC Capital Markets maintained their ‘neutral’ rating the firm but reduced the target price from $58 to $54, saying that the usage of Vectibix is expected to be limited to monotherapy in the near term. Worldwide estimate sales of the drug for 2007, 2008, 2009 and 2010 have been reduced by $70 million, $263 million, $293 million and $309 million, respectively.