Cancer risk, disease-modifying therapy, and age in multiple sclerosis: A retrospective population-based cohort study

Long-term population-based safety studies are needed to investigate cancer outcomes in people with multiple sclerosis (MS) treated with modern disease-modifying therapy (DMT).

To investigate if exposure to DMT increases the risk of invasive cancer in MS.

We used population-based administrative health data from Alberta, Canada between 2008 and 2018. DMT exposure was defined in two ways: first as exposure to any DMT, and second by DMT type (modulating, sequestering, depleting). Study outcome was time to first diagnosis of invasive cancer. Cancer risk was compared to the general population using standardized incidence ratios (SIRs) and to the unexposed MS cases using hazard ratios (HRs).

The analysis included 14,313 MS cases: 5,801 (40.5 %) were exposed to DMT. Median (interquartile range) follow-up was 8.4 (4.3, 10.4) years. Compared to the general population, there was no difference in cancer risk for the overall MS population (SIR: 0.94, 95 % confidence interval [CI]: 0.87, 1.02) or the DMT-exposed MS cases (SIR: 0.89; 95 % CI: 0.75, 1.05). Compared to unexposed MS cases, we found an interaction with age for exposure to any DMT (p = 0.001) and modulating DMT (p = 0.001), indicating that a difference in the risk of cancer associated with DMT depends on age. Cancer risk was not associated with exposure to sequestering DMT (HR: 1.28, 95 % CI: 0.78, 2.08) or depleting DMT (HR: 2.29, 95 % CI: 0.86, 6.14).

Cancer risk for MS patients was similar to the general population. In the MS population, the age-dependent effect of DMT for cancer risk suggests a higher risk of cancer with age 62 or older and a protective effect at younger age. Further investigation is required to clarify whether the interaction between DMT exposure and age is a causal effect.