A standard treatment for keeping inflammatory bowel disease in check increases the risk of infection-related cancers, but not enough to preclude its use, according to a study published Monday.

Thiopurine drugs are immunosuppressants commonly prescribed for Crohn's disease and ulcerative colitis, two different kind of inflammatory bowel disease (IBD).

Ulcerative colitis causes sores in the lining of the rectum and colon, while Chrohn's disease can attack anywhere in the digestive track.

Both disorders are linked to a malfunctioning of the immune system that results in an overabundance of white blood cells.

Earlier studies had shown that thiopurine -- also used to prevent organ and tissue rejection -- could, in transplant patients, lead to cancers associated with viral infection.

But little research had investigated whether IBD patients taking the drug ran a similar risk.

To find out, scientists led by Laurent Beaugerie of the Saint-Antoine Hospital in Paris analysed data on 19,486 patients in France with inflammatory bowel disorders.

Nearly 700 doctors provided details on drug treatment, incidence of cancer, and the number of deaths, with an average follow-up time of 35 months.

At the outset, 30 percent of the participants were taking thiopurine, 14 percent had discontinued treatment, and 56 percent had never received the drug. Over the course of the study, 23 new cases of lymphoma cancer were diagnosed.

Patients on thiopurine had a more than five-fold increased risk of contracting the disease compared to those who had never had the drug.

But overall, the absolute risk for those on thiopurine remained low -- less than one percent, the researchers reported in the British medical journal The Lancet.

The finding "does not undermine the positive risk-benefit ratio of these drugs," the study concluded.

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AFP 181102 GMT 10 09