Examining cancer risk in MS
Multiple sclerosis is a condition in which the normal function of the immune system is dysregulated. One of the important roles of the immune system is to patrol the body looking for damaged or abnormal cells, which can develop into malignancies. So if the immune system isn’t working as it should in MS, a potential concern is that people with MS may have a higher risk of developing some form of cancer.
Numerous studies have investigated this issue. Typically this involves examining national health databases to see if people with MS have a higher rate of cancers compared to the general population. For example, a recent study in Sweden reported that there was not an increased risk of breast cancer in younger women with MS, but there was a slightly higher risk of breast cancer after menopause (Hajiebrahimi and colleagues. PLoS One 2016;11:e0165027). However, on further analysis, this increased risk was seen only for women diagnosed in the period 1968 to 1980, and for those diagnosed after age 65. Moreover, the higher rate of cancer was only seen for early breast cancer (stage 0 or 1). So these findings suggest that breast cancer was being detected in women with MS because they were seeing their doctor more often (because of their MS), rather than because they have a higher breast cancer risk.
Other studies examining the possible association between MS and breast cancer have reported contradictory findings. A study in Switzerland found that breast cancer rates were higher in people with MS compared to the general population (Ajdacic-Gross and colleagues. Cancer Epidemiol 2016; 44:167-173). A study in the U.S. found the opposite: breast cancer was less common in women with MS (O’Malley and colleagues. J Neurol Sci 2015;356:137-141). These results suggest that the immune dysfunction seen in MS is not having a major impact on a person’s risk of breast cancer.
Many types of cancer appear to be less common in MS. Several studies have indicated that people with MS have a lower risk of lung cancer, stomach cancer, prostate cancer and ovarian cancer (Kyritsis and colleagues. Crit Rev Oncol Hematol 2016;98:29-34; Ajdacic-Gross 2016). A Canadian analysis of 38 studies found that the rates of pancreatic, ovarian, prostate and testicular cancer were lower than expected in people with MS (Marrie and colleagues. Mult Scler 2015;21:294-304).
If immune function influences cancer risk, a fair question is: do the immune-modulating therapies used to treat MS affect a person’s chances of develop a cancer?
This was investigated in a study of various MS therapies, including Gilenya, Aubagio, Tecfidera, Tysabri and Lemtrada (Pakpoor and colleagues. Neurol Neuroimmunol Neuroinflamm 2015;2:e158). The data used were from clinical studies, so a caveat is that the observation period was very short (cancers tend to take years to develop). Cancer rates were low (less than 1% both with treatment and a placebo) in most studies. The highest rate was seen with Copaxone, the lowest with Tecfidera and Aubagio. No increased risk of cancers with MS treatments was found.
However, it should be noted that studies don’t look at the complex interaction of MS, medications and lifestyle factors known to be cancer risks, such as smoking, sun exposure and diet. So to guard against additional medical problems developing, it’s important to keep to the monitoring schedule your MS doctor recommends, and to see your family doctor for regular check-ups.
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