NEW YORK (Reuters Health) – There’s no evidence that starting treatment with the anti-obesity drug orlistat raises the likelihood of developing colorectal cancer, at least in the short term, according to a population-based study.

“Our findings support the US Food and Drug Administration’s conclusion of no increased risk of colorectal cancer associated with the use of orlistat,” the researchers comment.

As they point out, “The FDA’s report was based on the negative results from pooled clinical trials and a small number of cases of colon cancer from the spontaneous adverse event reporting system. Our study, based on a large, population based healthcare database, represents people actually taking orlistat in the real world, who tend to be different from the participants in clinical trials.”

Lead author Jin-Liern Hong, at the University of North Carolina at Chapel Hill, and colleagues note that in preclinical studies orlistat was associated with increased numbers of colonic aberrant crypt foci, but whether these are precursors of colon cancer is controversial. Despite the reassuring evidence from clinical trials, they explain, concern remains because of the extensive use of orlistat worldwide.

The team therefore conducted a retrospective study using data from 1998 to 2008 in the UK Clinical Practice Research Datalink. They matched 33,625 individuals who started orlistat treatment to 160,347 patients who did not. The two groups were well balanced after propensity-score weighting.

There were 57 colorectal cancers documented in the orlistat group and 246 in the control group, the investigators found. This translated to an incidence rate per 100,000 person-years of 53 and 50 in the two groups, respectively — a non-significant difference with a hazard ratio of 1.11.

Moreover, there was no increased risk of colorectal cancer when analyses of the data were stratified by age, sex, BMI, or diabetes at baseline, according to the report in the British Medical Journal online August 27.

“Our findings,” the authors conclude, “provide evidence that use of orlistat does not alter the risk of colorectal cancer.”

Still, they caution, “The study is limited by the relatively short follow-up time, and we cannot exclude the possibility of adverse effects of long term orlistat use on risk of colorectal cancer.”

SOURCE: Risk of colorectal cancer after initiation of orlistat: matched cohort study
Br Med J 2013.