Bristol-Myers had offered to acquire the ImClone shares it does not already own in a deal valuing the company at $5.2 billion. ImClone called the offer too low.

ImClone also had said its board had been discussing the possibility of splitting the company in two, separating its Erbitux cancer treatment and its drug-development pipeline businesses.

Erbitux is approved for colorectal and head and neck cancer in the United States and Canada, while a recent approval for the drug in Japan and new lung cancer data are expected to drive sales.

ImClone said it believed the pipeline business "may be extremely valuable and significantly increase stockholder value as a separate business."

Activist investor Carl Icahn, chairman of ImClone and a large shareholder of the company, had said he opposed Bristol-Myers' offer because he believes it "greatly undervalues the company."

ImClone and Bristol were not immediately available for comment. JPMorgan declined to comment.

Also under debate is an ImClone antibody, IMC-11F8, that is under development. If approved for sale, ImClone has said the antibody "might have a significant competitive effect on Erbitux," and Bristol-Myers may have no rights to market that product.

Bristol previously termed its offer for ImClone "full and fair" and said it believed it has rights to the follow-on drug to Erbitux.

ImClone shares were up 4 cents $63.99 in morning Nasdaq trading. Bristol gained 2 cents to $22 on the New York Stock Exchange.

(Reporting by Jessica Hall, editing by Gerald E. McCormick)