NEW YORK — The company at the heart of the Martha Stewart stock scandal is in the midst of a bitter patent dispute that threatens its bottom line and has led some world-renowned cancer researchers into a courtroom for a highly unusual showdown.

A judge in Manhattan federal court is deciding who is the rightful owner of a patent used for ImClone Systems Inc.'s blockbuster cancer drug Erbitux. A team of three esteemed scientists from Israel who pioneered a cancer treatment technique claim a former colleague stole their idea and was credited on a patent now owned by Aventis Pharmaceuticals Inc. and licensed to ImClone.

At stake is the future of ImClone, the company whose founder, Sam Waksal, is serving a prison sentence for his role in the stock scandal that also ensnared Stewart.

Erbitux, initially approved to treat colectoral cancer and later expanded to treat head and neck cancer, has contributed heavily to ImClone's success, although the company is facing serious competition from a drug by rival Amgen Inc. that is expected to hit the market in the coming months. Still, ImClone posted robust earnings Thursday, thanks to strong sales of Erbitux, which provided about half of the company's total revenue.

But any future earnings could be clouded by the lawsuit.

In the 2003 suit, Yeda Research and Development Co. of Israel sued ImClone — which has an exclusive license for the formula used in Erbitux to inhibit tumor cells — and Aventis, claiming three of its researchers should be named as the inventors. The current patent names Dr. Joseph Schlessinger, chairman of pharmacology at the Yale School of Medicine, as the inventor along with six others, three of whom even the defense has agreed do not belong on the patent.

One of the Israeli researchers, Michael Sela, testified that he considers Schlessinger "a superb scientist, a very good lecturer," and had thought of him as a friend and colleague before "the bad moment."

"I have a problem with his ethics," said Sela, a professor for 56 years at the Weizmann Institute of Science in Rehovot, Israel. Schlessinger was a longtime researcher at the institute.

In recent weeks, U.S. District Judge Naomi Buchwald has heard testimony from Sela, Schlessinger and other top cancer researchers. She has not yet ruled, and it is not clear when she might do so. But she was critical of many of the arguments presented by lawyers for ImClone and Aventis during closing statements Wednesday.

The consequences could be huge for ImClone if Buchwald rules in favor of the Israeli researchers.

At one point Wednesday, plaintiffs' lawyer Nicholas Groombridge said ImClone stands to lose its exclusivity with the technique covered by the license if Yeda's scientists are credited, freeing Yeda to license the patent to other drug companies. If Schlessinger is taken off the patent — something the judge indicated was a possibility — ImClone would not have a license anymore for the drug, he said.

"I presume there would be a negotiation and a deal would be reached," Groombridge said. "It is not the intent of Yeda to keep anybody off the market."

A lawyer for Aventis later noted that one trial witness had remarked that hundreds of millions of dollars were at stake for Yeda and ImClone. Erbitux had U.S. sales of $413 million last year.

Several times, the judge indicated she believed ImClone and Aventis should have settled when Yeda approached the company before trial to seek a deal. "I cannot decide this based on what the economic consequences may be. That's the risk you take when you don't resolve it," she told the Aventis lawyer.

She seemed poised to at least put the Weizmann scientists on the patent, telling one defense lawyer: "One might wonder why you didn't put the Weizmann people on your patent in the first place."

Schlessinger is credited with providing an antibody that, when combined with chemo-therapy drugs, sometimes has stopped cancer from growing. But aside from the antibody, "everything else was ours," said Sela, the former president of Weizmann.

He said it was the other researchers, not Schlessinger, who came up with the idea to combine the antibody with the chemotherapy medication — which served as the framework for the invention of Erbitux.

Sela said he had never paid much attention to patents.

"I don't mind if I don't take a patent, unless it's stolen from me. Then I have to react," he said. "At the beginning, when I first saw it, I was in a state of shock. I mean, money is not important, but my name and my science, my honor demanded" that he be put on the patent.