Background: Findings regarding cancer risk in MSers have been inconsistent and few studies have explored the possibility of diagnostic neglect. The influence of a relapsing-onset versus primary progressive course on cancer risk is unknown.
Objective: This study examined cancer risk and tumour size at diagnosis in a cohort of MSers compared to the general population and we explored the influence of disease course.
Methods: Clinical data of patients with MS residing in British Columbia, Canada who visited a British Columbia MS clinic from 1980 to 2004 were linked to provincial cancer registry, vital statistics and health registration data. MSers were followed for incident cancers between onset of MS, and the earlier of emigration, death or study end (31 December 2007). Cancer incidence was compared with that in the age-, sex- and calendar year-matched population of British Columbia. Tumour size at diagnosis of breast, prostate, colorectal and lung cancers were compared with population controls, matched for cancer site, sex, age and calendar year at cancer diagnosis.
Results: There were 6820 MSers included, with 110 666 person-years of follow-up. The standardized incidence ratio for all cancers was 0.86 (95% confidence interval: 0.78-0.94). Colorectal cancer risk was also significantly reduced (standardized incidence ratio: 0.56; 95% confidence interval: 0.37-0.81). Risk reductions were similar by sex and for relapsing-onset and primary progressive MS. Tumour size was larger than expected in the cohort (P = 0.04).
Conclusions: Overall cancer risk was lower in MSers with multiple sclerosis than in the age-, sex- and calendar year matched general population. The larger tumour sizes at cancer diagnosis suggested diagnostic neglect; this could have major implications for the health, well-being and longevity of MSers.
“This study is important for several respects. MS differs from other systemic autoimmune diseases, such as rheumatoid arthritis, that is associated with a higher risk of cancer than the general population. The thinking is that inflammation is one of the drivers of cancer development, by its effect on DNA. More importantly is the implications this data has for pharmocovigilance, i.e. monitroing whether or not DMTs are associated with higher risks of cancer. A lot of the studies compare MSers to the general population; this is clearly not the correct comparator. We would have to do formal studies to assess cancer risk from the newer DMTs; the studies will have to compared exposed MSers with a control group of non-exposed MSers, for example those on IFNbeta or GA or not on any treatment.”