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.