Despite the lashing criticisms of his work, Dr. Croce has never been penalized for misconduct, either by federal oversight agencies or by Ohio State, which has cleared him in at least five cases involving his work or the grant money he receives.

At Ohio State, officials said they were unaware of Dr. Sanders’s charges against Dr. Croce until asked about them for this article. Now, in the wake of those and other questions from The Times, the university has decided to take a new look to determine whether it handled those cases properly. “The university is instituting an independent external review,” a spokesman, Christopher Davey, said in a statement, adding that the review “is not an indication that we have discovered any evidence of scientific misconduct or other issues raised in your inquiry.”

Whatever the outcome of that review, Mr. Davey said, decisions on research misconduct at Ohio State were based solely on “the facts and the merits of each individual case,” not a researcher’s grant money. Any other suggestion would be “false and offensive,” he said, adding that the university has “spent significantly more to support his research program than he has brought in from outside sources.”

During an interview in October, and in a later statement, Dr. Croce, 72, denied any wrongdoing, said he had been singled out in some of the accusations simply because he was a prominent figure, and largely placed the blame for any problems with figures or text on junior researchers or collaborators at other labs. Academic papers often have multiple authors, with the scientists who perform the hands-on work listed at the beginning and the senior scientists in charge named at the end.

“It is true that errors sometimes occur in the preparation of figures for publication,” Dr. Croce said in the statement, issued through the Columbus law firm Kegler Brown Hill & Ritter. Any mistakes with figures were “honest errors,” he said, adding that he did not condone plagiarism but that he must rely on co-authors to provide proper attribution.

Even before his arrival at Ohio State in 2004, Dr. Croce had stepped beyond the generally expected bounds of cancer research. In 1994, he joined the scientific advisory board of the Council for Tobacco Research, which the tobacco companies created to fight the public perception — supported by increasingly overwhelming scientific evidence — that smoking caused cancer. Dr. Croce said in the interview and the statement that he had always believed that smoking caused cancer.

During the same period, Dr. Croce and a colleague faced federal allegations that they had submitted false claims for payment of grant money for science that was never carried out and that was to be overseen by a scientist who had, in fact, left the United States and gone to Italy. After the case was combined with a second fraud investigation, a civil settlement forced Thomas Jefferson University in Philadelphia, where Dr. Croce worked at the time, to pay $2.6 million to the government. Neither Dr. Croce nor the other parties to the settlement admitted any wrongdoing in the case.