Viral pathogenesis research

Humans are not the only mammals susceptible to breast cancer. Some strains of mice, namely the house mouse (Mus domesticus) are prone to breast cancer which is caused by infection with the mouse mammary tumour virus (MMTV or "Bittner virus" for its discoverer Hans Bittner), by random insertional mutagenesis. This finding is taken to mean that a viral etiology of human breast cancer is at least possible, though there is no definitive evidence to support the claim that MMTV causes human breast cancer. For example, there may be critical differences between cancer pathogenesis in mice and people. The understanding of the role of MMTV or other viruses in human breast cancer is preliminary as of May 2007.

Factors with minimal or no impact on risk

Abortion

Studies in rats led to speculation that abortion may increase the risk of breast cancer because of hormones initiating breast tissue growth in early pregnancy. Some early interview and record based case-control studies indicated a possible correlation, but more recent record based studies and a large meta-analysis study do not support this association. The subject was examined by a National Cancer Institute (NCI) workshop in 2003, in response to the Bush Administration's alteration of the NCI's website to emphasize studies indicating a potential link. The NCI expert panel concluded that induced abortion is not associated with an increased breast cancer risk.

Deodorants

Much has been made of the possible contribution of aluminum-containing underarm antiperspirants to the incidence of breast cancer, since the most common location of a breast cancer is the upper outer quadrant of the breast. Aluminum salts, such as those used in anti-perspirants, have recently been classified as metalloestrogens. In research published in the Journal of Applied Toxicology, Dr. Philippa D. Darbre of the University of Reading has shown that aluminum salts increase estrogen-related gene expression in human breast cancer cells grown in the laboratory. Fortunately, this in-vitro association between aluminum salts and estrogen activity does not translate into an increased risk of breast cancer in humans. The lack of association between underarm deodorants and breast cancer has been the subject of a number of research articles.