Risk Factors with Uncertain, Controversial or Unproven Effect

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Antiperspirants
Internet e-mail rumors have suggested that chemicals in underarm antiperspirants are absorbed through the skin, interfere with lymph circulation, and cause toxins to build up in the breast and eventually lead to breast cancer. There is very little experimental or epidemiological evidence to support this rumor.

Chemicals in products such as antiperspirants are tested thoroughly to ensure their safety. One small study recently found trace levels of parabens (used as preservatives in antiperspirants), which have weak oestrogen-like properties, in a small sample of breast cancer tumors. However, the study did not look at whether parabens caused the tumors.

This was a preliminary finding, and more research is needed to determine what effect, if any, parabens may have on breast cancer risk. On the other hand, a recent large epidemiological study found no increase in breast cancer in women who used underarm antiperspirants or shaved their underarms.

Underwire bras
Internet e-mail rumors have suggested that bras cause breast cancer by obstructing lymph flow. There is no scientific or clinical basis for that claim.

Induced abortion
Several studies have provided very strong data that induced abortions have no overall effect on the risk of breast cancer. Also, there is no evidence of a direct relationship between breast cancer and spontaneous abortion (miscarriage) in most of the studies that have been published.

Breast implants
Several studies have found that breast implants do not increase breast cancer risk, although silicone breast implants can cause scar tissue to form in the breast. Implants do make it harder to see breast tissue on standard mammograms, but additional x-ray pictures called implant displacement views can be used to more completely examine the breast tissue.

Environmental pollution
A great deal of research has been reported and more is being done to understand environmental influences on breast cancer risk. The goal is to determine their possible relationships to breast cancer. Currently, research does not show a clear link between breast cancer risk and exposure to environmental pollutants, such as the pesticide DDE (chemically related to DDT) and PCBs (polychlorinated biphenyls).

Smoking
No studies have conclusively linked cigarette smoking to breast cancer, although some studies suggest it might increase breast cancer risk for women who start smoking in early adolescence. Of course, smoking affects overall health and increases the risk for many other cancers, as well as heart disease.

Night work
A few recent studies have suggested that women who work at night, for example, nurses on a night shift, have an increased risk of developing breast cancer. However, this increased risk has not yet been proven, and when further studies are conducted, this factor may be found to be unimportant.

Antibiotics
A recent study found that women who took antibiotics for any reason had a slightly higher risk of breast cancer. It is too early to tell if this association will hold up after other studies are done. Women who need to take antibiotics frequently may also have other health problems, and some researchers have suggested that it is these other conditions, rather than the antibiotics, that increase breast cancer risk.