With MS, the body’s immune system attacks myelin, the fatty, white substance that insulates and protects the nerves. MS is chronic and can be unpredictable and disabling.

“People with MS undergo an increased number of tests to monitor MS, making it more likely to detect other diseases,” said study author Emmanuelle Leray, PhD, of Rennes University in France. “We found an association between some types of cancer and MS which may have different explanations depending on a person’s age and the types of cancer. Overall, our study found the increased risk of cancer was quite small.”

For the study, researchers reviewed 10 years of data in the French national health care database. Researchers identified 140,649 people with MS and matched them for factors such as age, sex and residence to 562,596 people without MS. All participants were cancer free three years before the study. They were followed for an average of eight years.

During the study, 8,368 people with MS and 31,796 people without MS developed cancer.

Researchers determined there were 799 cancers per 100,000 person-years for people with MS and 736 cancers per 100,000 person-years for people without MS. Person-years represent both the number of people in the study and the amount of time each person spends in the study.

Researchers found people with MS had a 6% increased risk of developing any type of cancer regardless of age, sex and residence. They also found cancer risk was higher in those under 55 and lower in people 65 and older when compared to people without MS.

Researchers then looked at cancer types. People with MS had a 71% increased risk for bladder cancer, a 68% increased risk for brain cancer and a 24% increased risk for cervical cancer. However, they also had a 20% lower risk of prostate cancer, a 10% lower risk of colorectal cancer and a 9% lower risk of breast cancer.

“While our study found a higher risk for brain cancer, it may be due in part to earlier detection in those with MS since they regularly have brain scans which may detect cancers earlier, before a person has symptoms,” said Leray. “Frequent urinary tract infections in people with MS and the use of immunosuppressant drugs may contribute to their higher risk of bladder and cervical cancers.”

Leray added, “The lower risk for colorectal and breast cancers may be due in part to fewer people with MS getting screened for cancer in older age when they may be experiencing more MS symptoms. More research is needed, including studies that look at more closely at how cancer screenings may play a role.”

A limitation of the study was that researchers were unable to adjust for factors such as education, income, smoking and alcohol consumption since this information was not available in the national database.

The study was supported by the Rennes Institute of Clinical Neurosciences and the EDMUS-ARSEP Foundation.