ImClone Systems, still reeling from its defeat in the courts over rights to a patent covering colorectal cancer drug Erbitux, has been poleaxed by rival Amgen’s swift move to take out a license to the disputed intellectual property.

On Tuesday a US court set aside ImClone’s claim to a US patent that covers the use of epidermal growth factor receptor (EGFr) targeting monoclonal antibodies alongside conventional chemotherapy to treat cancer, saying that the evidence showed that it should be assigned to scientists at Yeda Research and Development, the commercial arm of Israel’s Weizmann Institute.

Amgen lost no time in capitalising on ImClone’s misfortune, particularly as the patent could have led to litigation between the two companies. Amgen’s competitor to Erbitux, called Vectibix (panitumumab), is currently submitted for approval as a third-line, single-agent treatment for colorectal cancer, but the company wants to quickly expand its indications to include combination therapy.

ImClone has said it will try to reverse the court ruling on appeal, invalidate the patent or negotiate an exclusive license to it with Yeda in a bid to protect Erbitux. But at present the company is facing the costs of mounting its appeal, potential damages on past sales of Erbitux and having to pay royalties on future sales, as well as a more robust competitive position for Amgen.

Vectibix is expected to mount strong competition to Erbitux because it is a fully-human antibody, which could mean that it is less prone to infusion reactions and allergic side effects than ImClone’s product. It could also be delivered at a smaller dose which could allow Amgen to offer a reduced price compared to Erbitux.

Either way, ImClone faces a period of uncertainly both externally and now internally, as the appointment of billionaire investor Carl Icahn to the board earlier this week will almost certainly lead to a management shake-up at the firm.

Chairman David Kies is already under pressure to step down, while ImClone is still looking for a permanent chief executive to replace the current interim incumbent – Joseph Fischer – who is the fourth person to hold the post in as many years.