Background:
We investigated cancer risk among patients with multiple sclerosis (MS) and whether variation by age at MS diagnosis helps to elucidate mechanisms underlying the previously reported reduced cancer risk. We also studied cancer risk among parents to ascertain if MS susceptibility genes may confer protection against cancer in relatives.
Methods:
Cox proportional hazards regression, adjusted for age, sex, area, and socioeconomic index, estimated cancer risk among 20,276 patients with MS and 203,951 individuals without MS, using Swedish general population register data. Similar analyses were conducted among 11,284 fathers and 12,006 mothers of patients with MS, compared with 123,158 fathers and 129,409 mothers of controls.
Results:
With an average of 35 years of follow-up, there was a decreased overall cancer risk among patients with MS (hazard ratio ฯญ 0.91, 0.87-0.95). Increased risks were observed for brain tumors (1.44, 1.21-1.72) and urinary organ cancer (1.27, 1.05-1.53). Parents of patients with MS did not have a notably increased or decreased overall cancer risk.
Conclusions:
The reduction in cancer risk in patients with multiple sclerosis (MS) may result from behavioral change, treatment, or we speculate that some immunologic characteristics of MS disease activity improve antitumor surveillance. The lack of association among parents indicates that a simple inherited characteristic is unlikely to explain the reduced cancer risk among patients with MS. MS is associated with increased risk for some cancers, such as of urinary organs and brain tumors (although surveillance bias may be responsible). Neurology ยฎ 2009;72:1170-1177 GLOSSARY CI ฯญ confidence interval; HR ฯญ hazard ratio; MS ฯญ multiple sclerosis.Cancer risk among patients with multiple sclerosis (MS) is important, as they may be subject to immunomodulatory therapies potentially altering cancer risk. A large Danish study 1 and some smaller studies 2-4 reported a lower overall cancer risk in MS, although there are contradictory results. 5 MS has been associated with a reduced risk for digestive, respiratory, prostate, and ovary cancers 1 and non-Hodgkin lymphoma 6 but increased risks for urinary tract and nasopharyngeal cancers. 1 Breast cancer risk has been reported as higher, 1,4 lower, 3 or unchanged. Besides assessing cancer risk in a nationally representative group of patients with MS diagnosed over several decades with long follow-up and general population-based controls, this article is concerned with establishing if any reduced cancer risk is due to changes following disease onset. This could include lifestyle changes following diagnosis, or immunologic changes due to disease activity: these influences may not be mutually exclusive and younger age at MS onset could confer greater