A pivotal trial of Amgen’s much-anticipated new colorectal cancer drug panitumumab has revealed that it can significantly improve survival when compared to best supportive care in patients whose cancer has progressed despite standard chemotherapy.

Panitumumab reduced the rate of disease progression by 46%, and significantly more patients were alive and free of progression at each time point in the study. After six months, 18% of the panitumumab group were alive and progression-free, compared to 5% of those on best supportive care, according to the results of the trial, which were presented at the American Association of Cancer Research conference in Washington DC.

Amgen filed for approval of panitumumab in the USA in late March and, if approved, it will compete head-to-head with ImClone Systems and Bristol-Myers Squibb’s Erbitux (cetuximab), which was cleared for colorectal cancer in 2004 and has just seen its indications extended to include head and neck cancer.

Sales of Erbitux by B-MS reached $413 million last year, while European marketer Merck KGaA made $258 million from the drug in the same period. Analysts have predicted that panitumumab, which is a fully human antibody and has a good tolerability profile, could achieve close to $2 billion in sales at peak.

“Panitumumab was well-tolerated in patients with metastatic colorectal cancer, with very few major adverse reactions," said Marc Peeters of Ghent University Hospital in Belgium, who led the Phase III study. In particular, Amgen’s drug showed no sign of causing the allergic reactions that can cause problems with antibody-based therapies.

But while panitumumab and Erbitux share a molecular target (the epidermal growth factor receptor) and will be direct rivals, both are likely to face competition from Genentech/Roche’s Avastin (bevacizumab), another colorectal cancer drug that was cleared in the USA in 2004. Roche reported $1.3 billion in Avastin sales last year, while Genentech said it made $1.1 billion from the drug, which blocks vascular endothelial growth factor.

$2.2bn Abgenix buy goes through

Meanwhile, Amgen said it had completed the purchase of Abgenix, its partner for panitumumab, for $2.2 billion in cash. The biotechnology giant noted the transaction would eat into earnings per share in 2006 and 2007, to the tune of 5 to 10 cents.

Amgen’s purchase of Abgenix means that it receives all the profit on sales of panitumumab, should it reach the market.