People with multiple sclerosis who are diagnosed with colorectal cancer may be at a higher risk of dying from cancer or other causes over the next six months to one year than people with colorectal cancer who do not have MS, according to a new study.

Researchers at the University of Manitoba, in Winnipeg, Canada, looked at health records for 338 people with MS and colorectal cancer who lived in Ontario and Manitoba, Canada. Each person was matched with four people who had colorectal cancer but did not have MS who were the same age and sex, and had the same year of cancer diagnosis, or 1,352 people. The participants were an average age of 65 when they were diagnosed with cancer.

The study found that people with MS were 45 percent more likely to die of any cause at six months after the cancer diagnosis than people without MS and 34 percent more likely to die of any cause at one year after diagnosis. After that point, the risk of death was the same for the two groups. People with MS were more likely to die of cancer than people without MS only at the six-month point after diagnosis, when their risk was 29 percent higher. The researchers adjusted for other factors that could affect risk of death, such as age, socioeconomic status and having other conditions like heart disease or diabetes.

Over five years, the fatality rate in Ontario was 16.4 deaths per 100 person-years for people with MS who died from any cause compared to 11.5 deaths for people without MS. Person-years take into account the number of people in a study as well as the amount of time spent in the study. In Manitoba, those numbers were 19.8 deaths per 100 person-years for people with MS and 15.4 deaths for people without MS.

Looking at deaths due to cancer, the fatality rate was 12.7 deaths per 100 person-years for people with MS in Ontario, compared to 9.9 deaths for people without MS. In Manitoba, those numbers were 13.6 for people with MS and 13.0 for people without MS.

A limitation of the study was that researchers may not have accounted for all other conditions people may have had in addition to MS and colorectal cancer.

According to the Centers for Disease Control, “colorectal cancer almost always develops from precancerous polyps (abnormal growths) in the colon or rectum. Screening tests can find precancerous polyps, so that they can be removed before they turn into cancer.” The CDC recommends regular screening, beginning at age 45, to prevent colorectal cancer and finding it early, when treatment works best.

The findings were published in the journal Neurology.