Multiple sclerosis and breast cancer
A frequent observation has been that people with multiple sclerosis generally have a lower risk of developing many forms of cancer compared to those in the general population (Nielsen and colleagues. Int J Cancer 2006;118:979-984; Lebrun and colleagues. Mult Scler 2008;14:399-405; Catala-Lopez and colleagues. Psychother Psychosom 2014;83:89-105). The reasons for this aren’t well understood.
One of the few exceptions is breast cancer. Women with MS appear to have a slightly higher risk of developing breast cancer compared to the non-MS population (Nielsen 2006; Midgard and colleagues. Acta Neurol Scand 1996;93:411-415; Sun and colleagues. Eur J Neurol 2014;21:238-244).
Why would women with MS have a higher risk of breast cancer?
Researchers have looked at various possible factors that may contribute to the risk. For example, women who have children earlier in life have a lower risk of breast cancer; conversely, breast cancer risk is higher for women who don’t have children or who have children later on. However, when these were taken into account, women with MS still had a higher rate of breast cancer (Nielsen 2006), suggesting that these lifestyle factors don’t play a major role.
Perhaps the most obvious factor to investigate is MS therapies – do they affect breast cancer risk? An important role of the immune system is to patrol the body looking for defective cells such as cancer cells, and MS therapies have the potential to alter this immune surveillance.
One study found that women with MS had a somewhat higher risk of breast cancer if they had been treated with immunosuppressive drugs (not the MS therapies commonly used) (Lebrun 2008). One analysis suggested an increased rate of breast cancer in women treated with Copaxone (Achiron and colleagues. Breast Cancer Res Treat 2005;89:265-270). As for the interferon drugs, one recent study reported a trend to a higher rate of breast cancer (Kingwell and colleagues. J Neurol Neurosurg Psychiatry 2014; epublished March 4, 2014), although an earlier study found no increased risk (Achiron 2005). According to the product labels, interferon use may be associated with a slightly higher rate of breast cancers, although this risk may decline over time; fibrous changes to the breast tissue may also occur. There is no evidence of an increased risk of breast cancer with newer drugs, such as Tysabri, Gilenya, Aubagio or Tecfidera.
So if MS therapies increase the risk, their effect appears to be minimal and other factors may be at work. One such issue was highlighted in a population study in British Columbia, Canada (Kingwell and colleagues. Brain 2012;135[Pt 10]:2973-2979). Overall, people with MS had a lower risk of many cancers, such as lung, colorectal and prostate. However, at the time a cancer was diagnosed, the size of the tumours was larger in people with MS compared to the general population. This suggested a not-so benign neglect. The idea was that without annual exams by the family doctor, breast self-examination and regular mammograms, the breast cancers that were occurring were being detected later. It may have been that once MS was diagnosed, doctors and the people themselves tended to forget about other health issues.
Mammograms are the best way to detect breast cancer early, although the best approach is a matter of controversy. The American Cancer Society recommends annual mammograms for all women aged 40 or older; others say that a mammogram every two years after age 50 is good enough (U.S. Preventive Services Task Force. Ann Intern Med 2009;151:716-726). However, one-third of women over 40 haven’t had a mammogram in the past two years, according to the U.S. National Health Interview Survey (Department of Health and Human Services. Health, United States, 2013. www.cdc.gov/nchs/data/hus/hus13.pdf#083).
The statistics are even worse for women with MS. The U.S. National MS Society estimates that only 1-2% of women with MS over age 40 have a mammogram in any given year (Multiple Sclerosis Sourcebook. Atlanta, GA: National Multiple Sclerosis Society; 1999), although substantially higher rates have been reported by some centres (Todd & Stuifbergen. Int J MS Care 2011;13:49-56). There may be many reasons, physical and psychological, for avoiding mammography. It can be difficult to get to a clinic, hard to get positioned in the machine, and uncomfortable undergoing the exam itself. A person may forget to ask their doctor about it, may be afraid of what they’ll find, or may feel that living with MS is trouble enough (Nosek & Howland. Arch Phys Med Rehabil 1997;78[12 Suppl 5]:S39-44; Todd 2011).
However, even women with MS-related disabilities have been shown to be able to perform breast self-examination, see their family doctor for non-MS health matters, and schedule regular mammograms – if the motivation is there (Paraska K. Int J MS Care 2012;14:142-147).
Vitamin D supplements may also be helpful in maintaining breast health. Laboratory studies have suggested that vitamin D can suppress breast cancer cells (Laplant & Knobler. American Academy of Neurology annual meeting 2014; abstract P6.176). And a preliminary study found that there was a very modest decrease in breast cancer risk in people taking 400 IU per day of vitamin D (Gissel and colleagues. J Steroid Biochem Mol Biol 2008;111:195-199). Although the evidence is very preliminary, a daily dose of vitamin D is an easy and inexpensive add-on to the regular MS medications. But it’s just not a substitute for seeing a doctor and undergoing regular cancer screening.
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