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.

Fertility treatments

There is no persuasive connection between fertility medications and breast cancer.

Phytoestrogens and soy

Phytoestrogens such as found in soybeans have been extensively studied in animal and human in-vitro and epidemiological studies. The literature support the following conclusions:

1. Plant estrogen intake, such as from soy products, in early adolescence may protect against breast cancer later in life.

2. Plant estrogen intake later in life is not likely to influence breast cancer incidence either positively or negatively.

It seems reasonable to conclude that soybean-based phytoestrogens are not a major contributor to the incidence of breast cancer.