Research suggests that data from over a quarter of cancer clinical trials may never reach the public domain.

Doctors use the results from trials to choose the best treatment for patients. But experts from the charity, speaking at the BA Festival of Science in Exeter, are concerned that their ability to do this may be hampered by inaccessible data.

They believe a comprehensive database of all clinical trials is needed to monitor the progress of research and ensure data is published.

Dr Richard Sullivan, Head of Clinical Programmes at Cancer Research UK, says: "The medical community needs to know the results of clinical trials to be able to view the entire picture of how a treatment works, how it compares to other therapies and what choices could serve patients best.

"It's disturbing to think that important information on clinical trials is being left to gather dust."

One study* looked specifically at 500 cancer clinical trials and found that 26 per cent had failed to fully publish five-years after presenting preliminary data at a leading American cancer conference.

Trial investigators cited lack of time and shortage of funds as their main reasons for not publishing.

The study also suggests that investigators may lose interest in trials where the treatment being tested was found to be no better than the standard and can experience difficulties with getting this kind of result published.

Dr Sullivan says: "If only positive results are published this can distort medical literature and leave doctors thinking a treatment is more effective than it actually is. This in turn can affect the validity and findings of subsequent reviews, treatment decisions and clinical practice guidelines."

Unpublished data may also slow down research efforts and lead to work being duplicated. Professor Fran Balkwill is Head of Translational Oncology at the Cancer Research UK Clinical Centre in London. Her team are responsible for making sure discoveries in basic science move into the clinic.

She says: "All scientists, whether clinical or not, have a responsibility to make sure their data is accessible to the wider community.

"If the results from trials never reach the public domain researchers could waste time and unknowingly repeat lines of inquiry that have already been proven unsuccessful."

Experts at the charity believe that, within the UK, a comprehensive database of cancer clinical trials is needed to track the progress of research and ensure that results are published when trials finish.

Dr Sullivan says: "Registries for cancer clinical trials exist but they are not compulsory and are far from being complete.

"There needs to be one comprehensive database so trials can be monitored and a wealth of information can be accessed from a central place."

* Krzyanowska, MK, Pintilie M, Tannock IF. Factors associated with failure to publish large randomised trials presented at an oncology meeting Journal of the American Medical Association 2003; 290: 495-501