Researchers involved in the so-called SEAS study - highlights of which were first released in July - said there was no credible evidence linking Vytorin to cancer and the higher number of cases seen in the trial was simply a fluke.

But an editorial in the influential New England Medical Journal, which published the full data from the Vytorin study online, said the safety of the drug was now in doubt and several leading doctors also expressed concerns.

The full report on the trial showed a total of 105 cancer cases among Vytorin patients compared with 70 taking a placebo.

That was an upward revision from the rates of 93 and 65 reported in July.

Lead investigator Terje Pedersen of Ulleval University Hospital in Oslo, however, said cross-checks with cancer rates in two much larger ongoing trials simply did not support the idea that Vytorin was linked to cancer.

Other leading cardiologists were not so sure.

'I am quite concerned,' Heinz Drexel, professor of medicine at the University of Innsbruck in Austria and spokesman for the European Society of Cardiology told Reuters. 'At the moment, I would not take ezetimibe myself.'

Ezetimibe is one of the two ingredients in Vytorin, alongside the established statin drug Simvastatin.

US lawmakers and regulators have already announced probes into the possible cancer link with Vytorin and shares in both the drugmakers have tumbled since July.

But the key for the companies - both of which say the finding is simply a statistical anomaly - will be doctors' reaction to the furore.

The New England Journal of Medicine added to the scepticism.

'Physicians and patients are unfortunately left for now with uncertainty about the efficacy and safety of the drug,' it said in an editorial.

It noted that ezetimibe interfered with the gastrointestinal absorption not only of cholesterol but also other molecules that could conceivably affect the growth of cancer cells.

Dr Pedersen said there was absolutely no evidence for such a cancer-causing mechanism. -- REUTERS