A new study has found some cancers to be slightly more frequent in people with multiple sclerosis than in people without MS. Types of cancers found to have a small increased risk include bladder, brain, and cervical cancers. The study does not prove that MS increases a person’s risk of cancer. It only shows an association. 

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

For the study, researchers at Rennes University, in France, reviewed 10 years of data in the French national healthcare 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 percent 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 percent increased risk for bladder cancer, a 68 percent increased risk for brain cancer and a 24 percent increased risk for cervical cancer. However, they also had a 20 percent lower risk of prostate cancer, a 10 percent lower risk of colorectal cancer and a 9 percent lower risk of breast cancer. 

The researchers said that while the study found a higher risk for brain cancer, it may be in part because of earlier detection in those with MS because they regularly have brain scans, which may detect cancers earlier, before a person has symptoms. 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.

The researchers also said the lower risk for colorectal and breast cancers may be because 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 because this information was not available in the national database.

The study is published in the journal Neurology.