No overall cancer boost with azathioprine for IBD

Last Updated: 2010-02-18 16:00:12 -0400 (Reuters Health)

By David Douglas

NEW YORK (Reuters Health) - Patients with inflammatory bowel disease (IBD) who have taken azathioprine have a higher risk for lymphoma but no overall increase in cancer risk, according to UK researchers.

Senior author Dr. Timothy R. Card told Reuters Health by email that as use of azathioprine and 6-mercaptopurine for IBD has become more common over the last few years, physicians have been concerned "that this treatment may increase the risk of malignancy for patients."

In a January 26th online paper in The American Journal of Gastroenterology, Dr. Card, of the University of Nottingham, and colleagues report on data from 15,471 IBD patients without cancer at baseline.

Over a mean of 6.4 years, 392 (2.5%) developed an incident cancer, excluding non-melanoma skin cancers.

In the group with cancer, 10.5% had received at least one prescription for azathioprine (or 6-mercaptopurine), compared to 12.7% of the group without cancer.

Although initial analysis indicated that azathioprine might have had a protective effect against cancer, this was no longer the case after adjustment for age and smoking (odds ratio, 1.04).

In line with previous findings, patients with at least one azathioprine prescription had an increased risk of lymphoma (odds ratio, 3.22) compared to never-users.

However, there was no significant excess of azathioprine use among patients with malignancy. This finding, the researchers write, "is clearly reassuring to those taking and prescribing this drug."

"Our paper gives further weight to the argument that the benefits of azathioprine use in IBD greatly outweigh its risks," they conclude.

In his comments to Reuters Health, Dr. Card added, "Our study confirms a previous observation that patients on these drugs are at increased risk of lymphoma, but finds no evidence that they have an increased risk of cancer overall."

But, he and his colleagues point out, "Whether this association is causal, or whether it is the inflammation that azathioprine is used to treat that actually causes lymphoma, we cannot determine from this study."

In the meantime, Dr. Card said, "We believe this should reassure physicians that use of these drugs as practiced in the 1990s at least -- when most of our data were collected -- is not putting their patients at risk of cancer."

Am J Gastroenterol 2010.