TRENTON, N.J. – A House committee investigating the safety and effectiveness of the popular cholesterol drug Vytorin and one of its components is turning up the heat on the drug's makers.

The chief executives of Merck & Co. and Schering-Plough Corp. already were facing a Thursday deadline to produce extensive data on a clinical study called SEAS that indicated a possible cancer risk from Vytorin, which combines Merck's Zocor, a statin, and Schering-Plough's Zetia, a different type of cholesterol fighter that is the component under suspicion.

Now the House Energy and Commerce Committee wants answers to more questions and is asking the companies to let committee staff question the key statistics expert who has analyzed data on cancer cases and deaths in the SEAS study and two other ongoing Vytorin studies.

In a letter sent to Merck CEO Richard T. Clark and Schering-Plough CEO Fred Hassan this week, the committee directs the companies to answer questions about the analysis and a report on it by a highly regarded statistics expert, Sir Richard Peto, co-director of the Oxford University Clinical Trials Service Unit.

The letter states the committee had expected “a complete assessment of Vytorin's association with cancer in the SEAS study,” but only got a five-page report, relayed by the Food and Drug Administration on Aug. 21, that contained little more information than what Peto already had released publicly.

“We are concerned that an esteemed scientific consultant to Merck and Schering-Plough may have generated a secret report to FDA,” wrote the committee chair, Rep. John Dingell, and the chair of its Subcommittee on Oversight and Investigations, Rep. Bart Stupak.

An FDA spokeswoman did not immediately respond to questions about the allegation. The agency also is investigating whether there's a cancer risk from Vytorin.

Rosemarie Yancosek, a spokeswoman for Schering-Plough, said the companies know of no other report sent to the FDA and will cooperate with the committee's latest information request. In an e-mail reply to questions from The Associated Press, she said the report sent to the FDA was prepared independently by Peto and university colleagues.

Those scientists published further data from their analysis in the New England Journal of Medicine Tuesday, concluding that available data from three studies “do not provide credible evidence of any adverse effect” from Zetia on cancer rates. The Journal's top editors, in an accompanying editorial, said the data so far can neither prove nor rule out a cancer risk from Vytorin, which went on sale in late 2004.

Yancosek wrote that the pharmaceutical companies have not yet complied with the House committee's Aug. 21 information request, but are preparing answers and will respond soon.

Those questions centered on any financial and other ties between the companies and the Oxford scientists.

Yancosek wrote that Peto does not work for her company, and it doesn't control his activities.

Meanwhile, both the House committee and the Senate Finance Committee have been investigating for months whether Merck and Schering-Plough Corp. delayed releasing results of another Vytorin study that showed it was no better at reducing plaque buildup in the arteries than just Zocor, which is available as a cheap generic.

Merck and Schering-Plough sell Vytorin and Zetia through a joint venture. The two drugs last year brought in $5.1 billion.