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Some cancers occurred more frequently in people with multiple sclerosis (MS) than in others, a retrospective study in France showed.

Overall cancer risk was higher in MS patients (HR 1.06, 95% CI 1.03-1.08) compared with matched controls, reported Chloe Pierret, MSc, of Rennes University in France, and co-authors.

Risks were higher specifically for bladder cancer (HR 1.71, 95% CI 1.54-1.89), brain cancer (HR 1.68, 95% CI 1.42-1.98), and cervical cancer (HR 1.24, 95% CI 1.12-1.38), the researchers wrote in .

They were lower for prostate cancer (HR 0.80, 95% CI 0.73-0.88), breast cancer (HR 0.91, 95% CI 0.86-0.95), and colorectal cancer (HR 0.90, 95% CI 0.84-0.97).

After stratification by sex, the overall higher risk of cancer was present only in women (HR 1.08, 95% CI 1.05-1.11 vs HR 1.01, 95% CI 0.97-1.06).

People with MS undergo more tests, making it more likely to detect other diseases, noted co-author Emmanuelle Leray, PhD, also of Rennes University. "While our study found a higher risk for brain cancer, it may be due in part to earlier detection in those with MS since they regularly have brain scans which may detect cancers earlier, before a person has symptoms," she said in a statement.

"Frequent urinary tract infections in people with MS and the use of immunosuppressant drugs may contribute to their higher risk of bladder and cervical cancers," Leray observed.

"The lower risk for colorectal and breast cancers may be due in part to fewer people with MS getting screened for cancer in older age when they may be experiencing more MS symptoms," she pointed out. "More research is needed, including studies that look more closely at how cancer screenings may play a role."

Previous research about cancer risk in MS has shown mixed results, possibly due to study design, cancer screening rates, or ascertainment bias, the researchers noted.

"Our study estimate is much lower than the one reported by the that did not match on residence," Pierret and colleagues wrote. "Regions in the north and northeast of France have higher MS prevalence, and they also have a higher prevalence of lifestyle-related cancer risk factors, such as smoking and alcohol drinking. This results in a potential overestimation of the cancer risk in people with MS if not adjusted for residence."

A recent Canadian study showed the incidence of breast and colorectal cancers was similar between people with and without MS, but MS patients had a higher incidence of bladder cancer and central nervous system cancer. Other research in Canada showed there was no increase in breast cancer mortality in MS patients.

In addition, some MS disease-modifying therapies come with cancer warnings. Cladribine (Mavenclad), for example, carries a for an increased risk of malignancy. Prescribing information for ocrelizumab (Ocrevus) includes a precaution about increased malignancy risk, including .

Pierret and colleagues reviewed data from 2012 to 2021 in the French national healthcare database, identifying 140,649 people with MS and matching them on age, sex, residence, insurance plan, and cohort entry date with 562,596 controls. All participants were cancer-free 3 years before the study.

Most participants (70.8%) were women, and the mean age at index date was about 47. Participants were followed for 7.6 years.

During the study, 8,368 people with MS and 31,796 people without MS were identified as having cancer. Cancer incidence per 100,000 person-years, standardized by age and sex, was 926 (95% CI 898-955) among people with MS and 872 (95% CI 858-886) among controls.

Excess risk was found only in MS patients younger than age 55 (HR 1.20, 95% CI 1.15-1.24). Estimates by age showed a linear trend with a decrease in risk as age at entry increased.

"This trend was found in all cancer locations," the researchers wrote. Fewer people with MS than controls were screened for breast, cervical, or colorectal cancer, with a pronounced difference among those ages 65 and older, they noted.

The study has several limitations, Pierret and co-authors acknowledged. The database did not contain physician diagnoses from outpatient visits, lab results, or self-reported disease history, so algorithms were used in some cases. Findings could not be adjusted for education, income, or lifestyle factors like smoking and drinking. The type of MS, disability level, and cancer stage at diagnosis also were unknown.

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