MONDAY, March 27, 2006 (HealthDay News) -- A pioneering study supports a theory that a widely used class of antidepressant drugs can also fight cancers, such as colorectal cancer, Canadian researchers report.
The drugs, called selective serotonin reuptake inhibitors (SSRIs), include such popular medications as Prozac, Paxil and Zoloft. The study was based on reports that serotonin, the body chemical linked to depression, also promotes the growth of cancer cells, said Dr. Jean-Paul Collet, professor of biostatistics and epidemiology at McGill University in Montreal.
To test the validity of those reports, Collet and his colleagues turned to an existing database of Saskatchewan residents enrolled in a prescription drug plan. They found about a 30 percent lower incidence of colorectal cancer among people who took high doses of SSRIs, compared to those who did not take the drugs. No such reduction was found in people taking the older class of tricyclical antidepressants.
The results might apply to other cancers as well, Collet said, "but we chose colorectal cancer because the colon is rich in serotonin." And while the results are very preliminary, he said the study had the advantage of producing results in just six months.
"Now, even knowing the limitations of our study, it is a very strong piece of information to identify how to conduct future studies to validate the results," he said.
The results appear in the April issue of the journal Lancet Oncology.
The study drew a measured response from Dr. Henrik Toft Sorensen, professor of clinical epidemiology at Aarhus University in Denmark, who wrote an accompanying editorial in the journal.
"It is an interesting paper, but the study needs to be replicated by other groups," Sorensen said. "I can't rule out that the results might be due to bias."
Until carefully controlled studies are done, "treatment of colorectal cancer should not be changed," he said.
Collet said: "The next step should be to study the effects of SSRIs in high-risk populations, such as persons with a family history of colorectal cancer, to see whether in this treatment we can find protection. Also, studies might be done in patients who have cancer, to see whether after surgery, we could reduce the rate of recurrence or metastasis [spread of cancer elsewhere in the body]."
Future studies would have to take into account such factors as diet, use of other drugs and the presence of diseases such as diabetes and inflammatory bowel disease, which can affect the risk of colorectal cancer, the researchers wrote.
If studies do confirm the cancer-fighting effects of SSRIs, that could boost sales of the already-popular drugs. About 100 million SSRI prescriptions are written each year in the United States, and the number of prescriptions in Canada rose from 3.2 million in 1981 to 14.5 million in 2000, the report said.
More information
The U.S. National Institutes of Health can tell you more about SSRI antidepressants.
