Cancer patients should talk to their oncologist if they would like to join the Add-Aspirin trial istock

The world's biggest clinical trial has launched in the UK, with researchers looking to discover if taking aspirin every day can stop cancer returning. The Add-Aspirin phase III clinical trial will examine over 11,000 cancer patients over 12 years in more than 100 centres across the UK.

Scientists will recruit patients who have had or are currently having treatment for bowel, breast, oesophagus, prostate and stomach cancer. They plan to compare two groups of people taking different doses of aspirin – either 300mg or 100mg – every day for five years, along with a control group taking a placebo.

Scientists hope to establish if taking a daily dose of aspirin can stop or delay cancers that have been treated from an early stage from returning – as well as finding out how the drug might do this. The trial is being funded by Cancer Research UK, the National Institute for Health Research and the MRC Clinical Trials Unit at UCL.

Ruth Langley, chief investigator at the MRC Clinical Trials Unit, said: "There's been some interesting research suggesting that aspirin could delay or stop early-stage cancers coming back, but there's been no randomised trial to give clear proof. This trial aims to answer this question once and for all. If we find that aspirin does stop these cancers returning, it could change future treatment – providing a cheap and simple way to help stop cancer coming back and helping more people survive.

"But, unless you are on the trial, it's important not to start taking aspirin until we have the full results, as aspirin isn't suitable for everyone, and it can have serious side-effects. Please speak to your oncologist or research nurse if you would like to join the Add-Aspirin trial."

Aspirin is known to help prevent heart attacks and strokes and some research suggests it can also prevent some types of cancer. However, taking aspirin every day can also cause serious side-effects, including ulcers and bleeding from the stomach. To ensure participant safety, the trial asks all those involved to take 100mg of aspirin once a day for eight weeks at the start of the study – a phase known as a run-in. Anyone who does not want to continue or who experiences side-effects at this stage would be advised to discontinue the trial.

Fiona Reddington, from Cancer Research UK, said: "Aspirin's possible effects on cancer are fascinating and we hope this trial will give us a clear answer on whether or not the drug helps stop some cancers coming back.

"This trial is especially exciting as cancers that recur are often harder to treat, so finding a cheap and effective way to prevent this is potentially game-changing for patients."