Incidence and mortality vary with race and social status. Incidence rises with improving economic situation, while mortality is tied to low economic status. In the US incidence is significantly lower and mortality higher among black women and this difference appears to persist even after adjustment for economic status. It is currently unclear if significant racial differences in incidence and mortality persist after adjustment for economic status between women of white, Hispanic and asian origin in the US.

Several studies have found that black women in the U.S. are more likely to die from breast cancer even though white women are more likely to be diagnosed with the disease. Even after diagnosis, black women are less likely to get treatment compared to white women. Scholars have advanced several theories for the disparities, including inadequate access to screening, reduced availability of the most advanced surgical and medical techniques, or some biological characteristic of the disease in the African American population. Some studies suggest that the racial disparity in breast cancer outcomes may reflect cultural biases more than biological disease differences. However, the lack of diversity in clinical trials for breast cancer treatment may contribute to these disparities, with recent research indicating that black women are more likely to have estrogen receptor negative breast cancers, which are not responsive to hormone treatments that are effective for most white women. Research is currently ongoing to define the contribution of both biological and cultural factors.

Part of the differences in incidence that is attributable to race and economic status may be explained by past use of hormone replacement therapy

Factors with inconclusive research

Tea

One research published in 2009 has show that moderate green or black tea consumption (three or more cups per day) can reduce breast cancer risk by 37% in women younger than 50 years old, comparing with women who drank no tea at all. But no association was found for overall women. However that study has been criticized for inaccuracy and another study found no substantial association between and tea consumption in the overall, but found a weak inverse association between caffeine-containing beverages and risk of postmenopausal breast cancer.

Specifically about green tea, one study has found significant inverse association between risk of breast cancer and green tea intake in Asian women who were low soy consumers.

1,3-Butadiene

1,3-Butadiene is an environmental factor that can be found in air pollution and can be produced by combustion engines, as well as petroleum refineries. It is found in cigarette smoke and is also used in the making and processing of certain synthetic rubber products and fungicides. The National Toxicology Program has labeled 1,3-Butadiene as definite human carcinogen. The EPA has stated that people are mainly put in contact with this chemical through the means of simple inhalation.

Mammographic density

Mammographic density refers to the relative proportions of radiodense area compared to the radiolucent area on a mammogram, which is basically an x-ray of the breast. The radiodense area on a mammogram is white and is associated with ductal and lobular epithelium, connective tissue and fluid in the breast. The radiolucent area is dark gray or black and is associated with fat in the breast. High mammographic density is associated with a higher risk of developing breast cancer, but the reasons for this link are not certain and are being studied.

Red No. 3

Red No. 3 is a coloring agent used in some foods. In laboratory tests human breast cell DNA was found positive for damage when put into contact with Red No. 3, which means that it is genotoxic.

Factors with minimal or no impact

Abortion

The abortion-breast cancer (ABC) hypothesis (supporters call it the abortion-breast cancer link) posits induced abortion increases the risk of developing breast cancer; it is a controversial subject and the current scientific consensus has concluded there is no significant association between first-trimester abortion and breast cancer risk.

Bras

There is no scientific evidence to prove that any kind of bra can cause cancer.

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.

Folic acid (folate)

The results of the studies about the influence of dietary folic acid on breast cancer have been contradictory.

Viruses

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 origin 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.

History

In past centuries, the development of breast cancer was most commonly seen as divine punishment or a trial. From ancient Greek medicine until the end of the 17th century, the dominant medical explanation was an imbalance of the four humors. By the start of the 18th century, humoralism had generally been rejected. Many other theories were put forward, often related to sexual activity: In 1713, Bernardino Ramazzini said that nuns developed breast cancer at a higher rate than married women because they did not engage in sexual intercourse, and the "unnatural" lack of sexual activity caused instability of the breasts; others countered that the cause was frequently too much sexual activity. Other theories from the 18th century included various sorts of problems with the movement of body fluids, such as lymphatic blockages, curdled breast milk or the transformation of pus left after an infection.

In modern times, women are more likely to blame themselves, perhaps deciding that their diet, childbearing history, decision not to breastfeed, or level of exercise is the cause.