Groundbreaking McGill research yields compelling resultsCould the black cloud of clinical depression have a silver lining? A recent study by McGill researchers shows that commonly prescribed anti-depressant medications known as Selective Serotonin Reuptake Inhibitors (SSRIs) may protect against developing colorectal cancer. The groundbreaking research was published in the April edition of the prestigious Lancet Oncology journal.
Previous work in mice demonstrated that SSRIs both retard the growth of transplanted human bowel tumours and make mice that are susceptible to developing colorectal cancer less likely to do so. "Serotonin has a stimulating effect on cell division and multiplication so [if] serotonin is a promoting factor, the logic for using antiserotonin drugs is strong," epidemiologist Jean-Paul Collet pointed out. "The strength of the study is that we started with a clear a priori hypothesis coming from animal studies. . . the question was to verify whether we would find the same type of association in human beings. What we found is that people with cancer had less use of SSRIs than the control subjects. This is why we think that SSRIs have a protective effect."
Photo: Claudio Calligaris
Russian doll syndromeThe study, funded by the U.S. National Institute of Health, was conducted with PhD student Wanning Xu and Professor Stanley Shapiro, a colleague of Collet's in the Department of Epidemiology and Biostatistics and Occupational Health, using the administrative databases of Saskatchewan Health and the Saskatchewan Cancer Agency registry. Although over 10,000 cancer patients and 40,000 age- and gender-matched controls were studied in the population-based, nested case-control study, it took Xu only about six months to perform the actual number-crunching.
There are some caveats to the results. "The study is large by number of patients but it is not an experimental study like a randomized clinical trial, [where] you administer a placebo or a true drug and follow patients prospectively. Randomized trials are the gold standard for evidence," Collet pointed out. Observational studies such as his can be biased by many uncontrolled factors. So in the conclusion, his Lancet paper notes "we support conducting more studies about this question and maybe studying SSRIs with high risk patients [who] because of genetic factors or polyposis would have a high risk of [developing] cancer. Another interesting population would be patients with cancer to see if SSRIs could prevent recurrence or metastasis."
Collet cautions that treating millions of people with SSRIs in the hope of preventing colorectal cancer in some hundreds of thousands would be a risky business. "This type of research is extremely useful to conduct more research to determine what is the real effect." Collet likens these studies to playing with nesting Russian babushka dolls: open one and there's almost always another one inside. He's confident there will be a definitive answer to the question of using SSRIs to prevent or treat colorectal cancer within 5 to 10 years, depending on international collaborative research networks and the attitude of the pharmaceutical companies involved.
Originally published in The McGill Reporter, March 30, 2006.