Prior research has found increased colon and breast cancer in patients with multiple sclerosis (MS), but that was not borne out in this current study.
Although previous reports have found associations between multiple sclerosis (MS) and breast and colorectal cancer, a new population-based study found that is not the case, although it did find a higher incidence of bladder cancer.
The authors of the current study noted that a 2015 review found cervical, breast, and gastrointestinal cancers had the highest incidence in MS. However, they noted that many studies in the review were not population based or had other limitations and that other recent research reported inconsistent findings about the relative risk of cancer in patients with MS.
The retrospective study, published Wednesday in Neurology, examined the health records of 53,984 people with MS and 266,920 individuals without MS in Manitoba and Ontario, Canada. The majority of both groups were female. The time period of the study stretched from 1998-2018, with incidence rate ratios pooled for 2 time periods (1998-2007 and 2007-2018).
Each patient with MS was matched by birth year, sex, and region with 5 individuals without the disease; researchers then linked the records to cancer registries to estimate incidence of breast, colorectal, bladder, and 12 other cancers.
After adjusting for factors like sex, education and socioeconomic status, researchers found that cancer incidence and mortality rates did not differ between individuals with and without MS for breast (HR, 0.92; 95% CI, 0.78-1.09) and colorectal cancer (HR, 0.83; 95% CI, 0.64-1.07).
However, bladder cancer incidence and mortality rates were 72% higher for patients with MS, they said. Looking at the years 2008-2017, the incidence of bladder cancer was 25 cases per 100,000 person-years in the group with MS, and 15 cases in the group without MS. The increased incidence of bladder cancer from 1998-2007, while not reaching statistical significance, was similar in magnitude and direction seen in later years.
"This is good news for people with MS, because earlier studies have shown a link between MS and breast and colorectal cancers," study author Ruth Ann Marrie, MD, PhD, of the University of Manitoba in Winnipeg, Canada, and a member of the American Academy of Neurology, which publishes Neurology, said in a statement.
Although the incidence of prostate, uterine, and central nervous system cancers differed between the MS and matched cohorts, mortality rates did not. This may suggest that prior research findings regarding those cancers "may reflect differences in ascertainment and this warrants further investigation to better understand delivery of cancer prevention and treatment efforts in this population," the authors wrote.
One limitation of the study is that although the results were adjusted for comorbidities, researchers were unable to account for differences in health behaviors such as smoking, diet and physical activity—all of which Influence the development of cancer. in addition, the study did not account for the possibility of disease-modifying therapies contributing to risk.
However, among the strengths of the study, the authors cited the large sample size—the 2 provinces encompass 42% of the Canadian population—and greater statistical power. In addition, as Canada has universal health care, both provinces have comprehensive, high quality, population-based administrative data and cancer registries that are not subject to recall bias.
"The increased risk of bladder cancer in people with MS may have to do with the fact that people with the disease are more likely to have urinary tract infections and use catheters," Marrie said. "However, more research is needed to confirm our findings."
Marrie RA, Maxwell C, Mahar A, et al. Cancer incidence and mortality rates in multiple sclerosis: A matched cohort study. Published online November 25, 2020. Neurology. doi: 10.1212/WNL.0000000000011219