Shares in Amgen have slipped on the news that its colon cancer drug Vectibix has failed in a late-stage clinical trial to improve survival for patients with head and neck cancer compared to chemotherapy.

The US biotech giant has presented top-line results from a 658-patient Phase III trial evaluating Vectibix (panitumumab) as a first-line treatment in patients with recurrent and/or metastatic squamous cell head and neck cancer. The data showed the addition of Vectibix to platinum-based chemotherapy did not result in a statistically significant improvement in overall survival, the primary endpoint, compared to chemotherapy alone [11.1 months versus 9.0 months).

Agen noted that secondary endpoints of progression-free survival (5.8 months versus 4.6 months) and objective response rate (36% versus 25%) were numerically improved with Vectibix but were not tested for statistical significance. Full results will be presented at the European Society for Medical Oncology congress in October in Milan.

Roger Perlmutter, head of R&D at Amgen, admitted that “the outcome of this study is disappointing”. However, he said that Vectibix “remains an important monotherapy treatment option for patients with metastatic colorectal cancer whose disease has progressed on other therapies”.

This is a blow considering that Amgen has had high hopes for Vectibix since it was launched in 2006. However its sales are pretty small (second-quarter revenue up to $72 million from $56 million) and last November, the drug in combination with chemotherapy did not significantly improve overall survival in patients newly-diagnosed with KRAS wild-type metastatic colorectal cancer, compared to chemotherapy alone.

Investors seem concerned that the possibility of getting Vectibix approved for other indications is looking bleak. The drug competes with Bristol-Myers Squibb/Merck KGaA/Eli Lilly’s colon cancer drug Erbitux (cetuximab), which is already approved for head and neck cancer.

Shares in Amgen ended the day down 3.6% to $53.69.