Results from studies of antidepressant use and cancer risk have been inconsistent and focused mainly on cancers of the breast and ovaries. The risk associated with colorectal cancers is unknown. In the USA, about 100 million prescriptions of antidepressants are written every year and SSRI are the most commonly used. Animal studies have suggested that SSRI reduce the growth of colorectal tumours. Therefore, researchers postulated that these drugs might reduce the risk of colorectal cancer in humans.
In the study, researchers identified 3367 cases with colorectal cancer and matched them for age, sex, and calendar time with controls without cancer. After adjustment for non-steroidal antiflammatory use during the same period and SSRI use 6-10 years before diagnosis, they found a decreased risk of cancer for those taking a high (>6.0x10-6 mol per day) SSRI dose 0-5 years before diagnosis.
Prof Collet states: "Further investigation is needed, with more complete assessment of confounders such as lifestyle factors, use of drugs, and comorbidity that might affect the occurence of colorectal cancer".
In an accompanying Reflection and Reaction, Prof Henrik Toft Srensen (Aarhus University Hospital, Aarhus, Denmark) comments that data from the study "provide interesting insights, but until trial data is available, clinicians should not consider SSRI use solely for chemopreventive purposes".