Incidence of malignancy in multiple sclerosis: A cohort study in the Danish Multiple Sclerosis Registry

Background The association between multiple sclerosis and malignancy is controversial and a current appraisal is needed. Objective To determine the incidence of malignancy in patients with multiple sclerosis compared with the general population and in relation to disease-modifying therapy. Methods Patients with multiple sclerosis (1995 - 2015) were matched by birth year and sex to individuals without multiple sclerosis in the general population. Patients with multiple sclerosis initiating disease-modifying therapy were evaluated using landmark period analysis. Malignancy risk was assessed by incidence rates, incidence rate ratios, and standardised incidence ratios. Results The standardised incidence ratio of any malignancy (excluding non-melanoma skin cancer) in patients with multiple sclerosis (n = 10,557) was 0.96 (95% CI 0.88 - 1.06), and there was no increased incidence of specific malignancy types compared with the general population cohort (n = 103,761). At the 48-month landmark period, the age-adjusted incidence per 100,000 person-years of any malignancy (excluding non-melanoma skin cancer) was 436.7 (95% CI 361.0 - 512.4) in patients newly treated with immunomodulator-only and 675.1 (95% CI 130.4 - 1219.9) in patients newly treated with immunosuppressant-only. Conclusions There was no increased incidence of malignancy overall or by type in patients with multiple sclerosis compared neither with the general population nor in relation to disease-modifying therapy.