Does multiple sclerosis affect survival rate after colorectal cancer diagnosis?

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 multiple sclerosis, according to a study published in the September 15, 2021, online issue of Neurology®, the medical journal of the American Academy of Neurology.

“These results warrant further investigation to determine what factors may lead to shorter survival times,” said study author Ruth Ann Marrie MD PhD of the University of Manitoba in Winnipeg, Canada, and a member of the American Academy of Neurology. “Are people with multiple sclerosis less likely to receive cancer treatment? Or are they less able to tolerate the effects of chemotherapy? Are factors specific to multiple sclerosis involved? How accommodating is the cancer care system for people with disabilities? These are among the many questions that need to be investigated.”

For the study, researchers looked at health records for 338 people with multiple sclerosis and colorectal cancer who lived in Ontario and Manitoba, Canada. Each person was matched with 4 people who had colorectal cancer but did not have multiple sclerosis, were the same age and sex, and had the same year of cancer diagnosis (1,352 people). The participants were an average age of 65 when they were diagnosed with cancer.

The study found that people with multiple sclerosis were 45% more likely to die of any cause at 6 months after the cancer diagnosis than people without multiple sclerosis and 34% 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 multiple sclerosis were more likely to die of cancer than people without multiple sclerosis only at the 6-month point after diagnosis, when their risk was 29% 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 5 years, the fatality rate in Ontario was 16.4 deaths per 100 person-years for people with multiple sclerosis who died from any cause compared to 11.5 deaths for people without multiple sclerosis. 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 multiple sclerosis and 15.4 deaths for people without multiple sclerosis.

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

“Understanding more about the factors involved in treating cancer in people with multiple sclerosis and their outcomes will be helpful for people with multiple sclerosis and their doctors as they balance the benefits of cancer treatment with the potential adverse effects and consider life expectancy and quality of life,” Marrie said.

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

The study was supported by the multiple sclerosis Society of Canada.