US biotechnology group ImClone saw its shares drop 13% to close at $28.05 yesterday, as a flurry of activity on the Nasdaq was sparked by news of the group’s decision to take itself off the shelf and remain independent.

ImClone, which makes the cancer therapy Erbitux (cetuximab), ended its six-month search for a suitor yesterday, changing track to find a new Chief Executive instead and inviting US billionaire Carl Icahn, who owns around 10% of the group, to join its board.

Explaining the decision, Joseph Fischer, Interim Chief Executive Officer of the group, said: “The alternatives available, including bids received for the acquisition of the company, did not match the value potential of ImClone Systems as an independent company. This decision was made in light of significant improvements in the top- and bottom-line performance of the company…and…numerous opportunities for growth.”

News that the New York-based firm had put itself up for sale earlier this year fuelled investor enthusiasm and shares surged, but expectations for a long list of potential buyers were soon quashed as it became clear that interest in ImClone was not that great.

Industry observers believe that potential buyers may have been put off by the unsteady future of the group’s flagship drug Erbitux, which could soon face strong competition if Abgenix and Amgen’s rival drug, Vectibix (panitumumab), gets the nod form US regulators, as well as growing concern its patent protection may be weaker than previously thought.