MS May Not Affect Breast Cancer Survival, Study Suggests

Women with multiple sclerosis (MS) diagnosed with breast cancer are not at a higher risk of dying from cancer than women without the neurodegenerative disorder, according to a Canadian population-based study.

However, 10 years after their breast cancer diagnosis, women with MS were 28% more likely to die from any cause than those without MS.

“It is reassuring that MS does not appear to increase risk of death from the cancer itself,” Asaff Harel, MD, a neurologist at Lenox Hill Hospital in New York who wasn’t involved in the study, said in a press release.

“The increase in death rate from ‘any other cause’ could be due to a number of reasons that may not be due to breast cancer itself or its treatment,” and may be “consistent with the slight decrease in life expectancy that exists with MS,” Harel added.

Despite its strengths, the study was restricted to two Canadian provinces and was unable to adjust the results for race or ethnicity, which can influence breast cancer survival.

As such, “future studies are needed to confirm these findings in women in other countries, and identify the factors specifically related to MS that are associated with worse outcomes,” Ruth Ann Marrie, MD, PhD, the study’s first author and the director of University of Manitoba’s MS Clinic in Winnipeg, Canada, said in a separate press release from the American Academy of Neurology.

The study, “Breast Cancer Survival in Multiple Sclerosis: A Matched Cohort Study,” was published in the journal Neurology.

“Although multiple sclerosis and its complications remain the most common cause of death in people with MS, cancer is the second or third most common cause of death,” Marrie said.

In a previous Canadian population-based study, Marrie and her colleagues at Manitoba and Ontario’s universities found that MS patients were at a higher risk of developing bladder cancer, but not breast or colorectal cancer — two of the three most common types in this patient population.

In the most recent study, they looked at “whether survival rates for women after a breast cancer diagnosis were different for those with MS and those without it,” Marrie said.

The researchers retrospectively analyzed the health records of 779 women with MS and 3,116 women with breast cancer, but not MS, matched for age, cancer diagnosis year, and region in Manitoba and Ontario.

These women were diagnosed with breast cancer at a mean of 57.8 years old, and the tumor had not spread to distant areas in the body in most (70%) cases with available cancer stage information.

The team then compared the 10-year mortality rates from all causes and specifically from cancer between the two groups. The results were adjusted for potential influencing factors such as age at cancer diagnosis, length of cancer diagnosis period, income, region, and coexisting conditions (comorbidities).

Data showed that cancer-related mortality rates were similar between women with MS and those without the neurodegenerative disease, suggesting that MS does not affect breast cancer survival.

However, women with MS had a 28% higher chance of dying from any cause than those who did not have MS. Particularly, there were 3.79 cancer-related deaths per 100 person-years in the MS group, compared with 2.98 deaths in the group without MS. Person-years refers to the gathered years of observation of all participants.

While the reasons behind this increased risk of all-cause death in the MS group still need to be clarified, data from the Ontario province suggested that it may be related to increased physical disability.