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Antidepressants May Cut Colon Cancer

Study: Colorectal Cancer Rarer in People Taking SSRI Antidepressants
By
WebMD Health News
Reviewed by Louise Chang, MD

March 27, 2006 -- A certain group of antidepressants may lower the odds of developing colon cancer, new research shows.

But experts haven't proven that those antidepressants fight colon cancer, so they're not recommending those drugs for that use.

The findings, published in The Lancet Oncology, come from more than 3,367 colon cancer patients in Canada's Saskatchewan province. Canadian researchers compared those patients with more than 13,400 people without colorectal cancer, making sure that cancer patients and the comparison group had similar backgrounds.

Colorectal cancer diagnoses were rarer in people taking high, daily doses of selective serotonin reuptake inhibitor (SSRI) antidepressants in the past five years, the study shows.

It's not clear if the SSRIs lowered colorectal cancer risk or if some other factor was at work, note the researchers. They included Wanning Xu, MSc, of Montreal's McGill University and Sir Mortimer B. Davis Jewish General Hospital.

Depression Drug Data

SSRIs are widely used to treat depression. Tests done on animals suggest that SSRIs might slow the growth of colorectal tumors, write Xu and colleagues.

The researchers didn't directly test SSRIs for colorectal cancer prevention. Instead, they noted patterns in antidepressant use and colon cancer cases among the study's participants from 1991 to 2000.

High, daily SSRI doses for up to the five previous years were tied to lower colon cancer risk. That pattern didn't hold for SSRI use prior to that (six to 10 years earlier).

Tricyclic antidepressants -- a different class of drugs than SSRIs -- weren't clearly linked to colorectal cancer risk, the study also shows.

What's at Work?

Perhaps SSRIs kill off colon cancer cells or stop those cells from spreading, write Xu and colleagues. But they're far from certain of that.

The researchers adjusted for participants' age, sex, and use of prescription nonsteroidal anti-inflammatory drugs (NSAIDs). The results still held.

But Xu's team couldn't take into account all possible influences on colon cancer risk. For instance, they didn't track over-the-counter NSAID use (such as aspirin), diet, smoking, alcohol use, obesity, or physical activity.

Cancer is complex, and it's hard to pinpoint exactly why someone did or didn't get cancer.

"An observational study, such as that by Xu and colleagues, can be difficult to interpret," states a journal editorial. Until antidepressants are directly tested against colorectal cancer in people, doctors shouldn't consider prescribing SSRIs just to prevent colorectal cancer, writes editorialist Henrik Toft Sorensen, MD, PhD.

Sorensen, who wasn't involved in Xu's study, works in Aarhus, Denmark, at Aarhus University Hospital's clinical epidemiology department.

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