ImClone Systems has dismissed Bristol-Myers Squibb improved offer to buy the firm and done so in quite a spectacular manner.

The New York-based major is now offering $62 per share, up from $60, for the 83% stake it does not already own in the firm. This latest bid values the US biotechnology company at around $4.7 billion (instead of $4.5 million) but this time B-MS is going straight to ImClone shareholders after chief executive James Cornelius fired off a cutting letter to Carl Icahn, the chairman of ImClone.

That letter saw Mr Icahn and his board accused of a “lack of transparency” which has “created a protracted period of uncertainty among your stockholders, employees and other constituents which could hurt the intrinsic value of ImClone’s assets”. To say this has not gone down well with Mr Icahn is an understatement and his letter in response is a humdinger.

He said that Mr Cornelius’ letter “contains inaccuracies which are misleading to our shareholders” and that there have not been any meaningful discussions concerning B-MS’ proposals “have no basis in fact”. During the last few weeks, “we told you we would be happy to meet if you wished to increase your offer to which you replied you had no intention to do”, Mr Icahn.

He then goes on to note that he informed B-MS, and indeed the media at large, that a large pharmaceutical company had offered $70 per share, subject to due diligence. The diligence will be over on Sunday, September 28 and “in light of these facts, your hostile tender of $62, at this time, seems absurd”, he said.

Mr Icahn was not finished yet though. He wrote: “If you wish to make your attorneys wealthier, I can show you more productive ways to do so. Or, if you simply want publicity, I can also help you in that regard without your having to make unnecessary expenditures”.

So it looks like the fight to get further control of the cancer drug Erbitux (cetuximab), which the two companies co-develop and co-promote in the USA, still has a lot of legs. In stockprice terms, however, it looks like Mr Icahn is winning as ImClone closed up 6.9%, at $63.51, while B-MS dipped 1.8% to $20.26.