The concealment often happens during the early stages of a drug's trial, usually when it is being tested on animals-and it often creates false hope as well as being a waste of money as expensive human studies are then initiated.
But only around 5 per cent of 'promising' cancer drugs and 20 per cent of heart drugs are ever licensed, suggesting the concealment is commonplace, say researchers from McGill University in Canada.
The practice came to light when the researchers looked at all the studies on sunitinib, which targets kidney cancer. They discovered that animal studies that reported little or no benefit were concealed; with only the positive studies being published, the cancer-fighting effects of the drug were over-estimated by 45 per cent.
The researchers' suspicions were first raised when early studies of sunitinib were showing that the drug was effective against a range of cancers, a result that "strains credibility", said lead researcher Dr Jonathan Kimmelman.
(Source: eLife, 2015; 4: doi: 10.7554/eLife.08351)