Assessment of cancer risk with β-interferon treatment for multiple sclerosis

Objective The risk of cancer after exposure to the beta-interferons (IFN beta s) for multiple sclerosis (MS) has not been established. We assessed whether IFN beta treatment for MS is associated with cancer risk or the risk of specific cancers in a population-based observational study. Methods The British Columbia MS database was linked to the provincial Cancer Registry, Vital Statistics death files and Health Registration files. Using a nested case-control design, MS cancer cases were matched with up to 20 randomly selected MS controls at the date of cancer diagnosis by sex, age (+/-5 years) and study entry year using incidence density sampling. Associations between treatment exposure and overall or specific (breast, colorectal, lung and prostate) cancers were estimated by conditional logistic regression, adjusted for MS disease duration and age. Tumour size at cancer diagnosis was compared between treated and untreated patients using the stratified Wilcoxon test to explore potential lead time bias. Results The cohort included 5146 relapsing-onset MS patients and 48 705 person-years of follow-up, during which 227 cancers were diagnosed. Exposure to IFN beta was not significantly different for cases and controls (OR 1.28; 95% CI 0.87 to 1.88). There was a non-significant trend towards an increased risk of IFN beta exposure in the breast cancer cases (OR 1.77; 95% CI 0.92 to 3.42), but no evidence of a dose-response effect. Tumour size was similar between IFN beta treated and untreated cases. Conclusions There was no evidence of an increased cancer risk with exposure to IFN beta over a 12-year observation period. However, the trend towards an association between IFN beta and breast cancer should be investigated further.