Patients with multiple sclerosis (MS) have a decreased overall cancer risk but have a higher risk of brain tumors and urinary organ cancer, according to a study published in the March 31 issue of Neurology. The lack of cancer risk among patients with MS likely does not result from an inherited characteristic, but rather from a behavioral change, treatment, or immunologic characteristic that improves antitumor surveillance, researchers reported.
Shahram Bahmanyar, MD, PhD, of the Clinical Epidemiology Unit in the Department of Medicine at Karolinska Institute in Karolinska Hospital in Stockholm, and colleagues estimated the disease risk among 20,276 patients with MS and 203,951 controls using data from the Swedish general population register. Similar analyses were completed among 11,284 fathers and 12,006 mothers of patients with MS, and also 123,158 fathers and 129,409 mothers of controls. The average length of follow-up was 35 years.
Overall, there was a decreased risk of cancer among patients with MS (hazard ratio [HR], 0.91). The risk for women was especially low. Follow-up beginning at the time of MS diagnosis showed little change (HR, 0.88). The risk was lower when, to ensure diagnostic accuracy, the analysis was restricted to MS register subjects and the relevant comparisons population (HR, 0.63). However, increased risks were observed for brain tumors (HR, 1.44) and urinary organ cancer (HR, 1.27). The average age of brain tumor diagnosis among patients with MS was 51.4, compared with 53.2 in the comparison group. An overall lower risk was observed among those who were diagnosed at earlier ages. Those diagnosed at age 20, between 20 and 34, and older than 34 had HRs of 0.32, 0.64, and 0.92, respectively. This effect was more pronounced among women, and an interaction test of age by gender produced a statistically significant HR of 0.974.
The overall cancer risk among parents of those with MS was not notably increased or decreased. Analysis of specific cancer sites did not show a protective or risk pattern. A modest increase for cancers of bone, kidney, and lymphoma among fathers was observed, along with an increase of endocrine cancers among mothers. “The lack of association among parents indicates that a simple inherited characteristic is unlikely to explain the reduced cancer risk among patients with MS,” Dr. Bahmanyar and colleagues stated.
“The lower cancer risk among patients with MS could be associated with lifestyle changes, treatment, disease-related activity, or a combination of these factors,” Dr. Bahmanyar and the study group suggested. Patients with MS often have a lower body mass index, which is a risk factor for some types of cancer. The researchers also speculated that cancer protection may result in part from the increase in systemic autoimmune responses against myelin antigens observed among patients.
“If autoimmune cells such as these react specifically against tumor autoantigens, this could represent an effective tumor defense mechanism,” the authors reported.
—Laura Sassano