People with multiple sclerosis (MS) are at a higher risk of developing and dying from bladder cancer than people without the neurodegenerative disorder, according to a Canadian population-based study.
However, no differences were found between MS patients and unaffected individuals in terms of their risk of breast and colorectal cancers — two of the three cancer types most prevalent in this patient population.
“This is good news for people with MS, because earlier studies have shown a link between MS and breast and colorectal cancers,” 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 press release.
“While we did not find that link, our study did show that people with MS had a 72% greater risk of developing bladder cancer,” Marrie said, noting that this may be associated with the fact that MS patients “are more likely to have urinary tract infections and use catheters.”
Despite its strengths, the study was unable to adjust the results for lifestyle factors, such as smoking, diet, and physical activity, or the use of MS disease-modifying therapies (DMTs) — all of which may potentially influence cancer development.
As such, “more research is needed to confirm our findings,” said Marrie, also a professor of medicine and community health sciences at the university, and a member of the American Academy of Neurology.
The study, “Cancer incidence and mortality rates in multiple sclerosis: A matched cohort study,” was published in the journal Neurology.
A previous review study, published in 2014, had shown that cervical, breast, and digestive cancers had the highest incidence among people with MS. Of note, incidence refers to the proportion of patients developing a disease during a particular period of time.
However, many of the evaluated studies were not population-based, and research since then has reported inconsistent findings regarding the relative risk of cancer in this patient population.
To clarify this research, Marrie and her colleagues at Manitoba and Ontario’s institutes and universities conducted a population-based study comparing the incidence of several cancers and cancer-specific mortality rates between MS patients and unaffected individuals (in a 1-to-5 proportion).
The team retrospectively analyzed the health records of 53,984 MS patients and 266,920 age-, sex-, and region-matched people without the disease in two Canadian provinces: Manitoba and Ontario.
The records were then linked to cancer registries to estimate incidence and the mortality rate of breast, colorectal, bladder and 12 other cancers among the two groups. The results were adjusted for potential influencing factors such as sex, age, education, socioeconomic status, and simultaneous health conditions (comorbidities).
Data showed that cancer incidence and mortality rates did not differ between people with and without MS for breast and colorectal cancer. However, people with multiple sclerosis had a 72% greater risk of developing bladder cancer than those without MS.
The 2008–2017 incidence of bladder cancer was 25 new cases per 100,000 person-years (the gathered follow-up years of all patients in the study) in the MS group, compared with 15 new cases in the group without MS. Notably, people with MS also showed higher bladder cancer-associated mortality rates.
Moreover, while the incidence of prostate, uterine, and central nervous system cancers differed between the MS and matched study groups, mortality rates did not.
As such, previously “reported differences in the incidence of some cancers in the MS population may reflect ascertainment differences rather than true differences,” the researchers wrote.
Among the study’s limitations were its inability to account for potentially influencing factors of cancer risk such as lifestyle behaviors and the use of specific DMTs. Of note, some of these therapies have been associated with a higher cancer risk.
The team noted, however, that the study, supported by the MS Society of Canada, had several strengths, including its large sample size, greater statistical power, and the use of high-quality, population-based data.
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