Registration of Increased Risk of Brain Cancer after the Diagnosis of Multiple Sclerosis

Background: We studied the cancer comorbidity of 18,212 Danish Multiple Sclerosis (MS) patients. Methods: Using data from the Danish National Patient Registry we identified all persons with a first-time MS diagnosis during 1980-2013. Cancer outcomes of the study cohort were ascertained using diagnoses from the Danish Cancer Registry. Patients with cancer prior to MS were excluded. We computed standardized incidence ratios with 95% confidence intervals calculated as the number of observed cancers relative to the expected based on national incidence rates by sex, age and calendar year. Results: All sites of cancers in the CNS were significantly increased, namely cancers of 1) membrane of the brain and spinal meninges, 2) brain, as well as 3) spinal cord, cranial nerves and central nervous system. MS is a disease of the CNS, and the 3 CNS cancer groups were individually significant. Several other cancers were also increased, namely 1) overall cancer, 2) urinary bladder cancer, 3) metastases and non-specified cancer in lymph nodes and 4) basal cell carcinoma. Conclusion: Multiple sclerosis is associated with increased registration of a range of cancers, in particular in the period following debut of MS. The results may be due to detection bias and misregistration. Finally, the results could be due to confounding.