What Causes Breast Cancer?

What Causes Breast Cancer?

Breast cancer is the most common malignant cancer in women, taking the lives of about 40,000 women a year in America alone. According to the Centers for Disease Control, there are an average of nearly 200,000 women living with breast cancer on any given day in America. Breast cancer is one of the deadliest cancers, with only lung cancer killing more women than breast cancer. So what causes breast cancer?

Researchers do not agree about the root causes of breast cancer. Let’s look at a few possible causes of breast cancer, risk factors, and other things associated with the development of this deadly disease.


What Causes Breast Cancer?

Being a female is the biggest risk factor for developing breast cancer. Men do develop the disease, but breast cancer is as much as 100 times more common in females.


A person’s risk of developing breast cancer increases with age. As much as 70% of deadly invasive breast cancer occurs in women who are 55 or older.


While much is made of the genetic component to breast cancer, only about five percent of breast cancer diagnoses are linked directly to mutations in specific genes. Women with certain genetic mutations have a high risk (as high as 80%) of developing breast cancer during their life, but very few women have these genetic mutations.

Race or Ethnicity

Caucasian women are more likely to get breast cancer than African-American women, but African-American women are far more likely to die from breast cancer. Why the discrepancy? Doctors think it is two-fold–African-American women have tumors that are more aggressive and grow fast, but the reason behind that is unknown. Another factor is sheer poverty–poor African-American women have less access to doctors.

Along these same lines, Asian, Hispanic, and Native-American women have a much lower risk of developing and dying from breast cancer.

Breast type

Certain breast types seem more likely to develop cancers. Having very dense breast tissue is a sign of a high gland-to-fat tissue ratio, and women with these high ratios of glands to fat have a much higher risk of developing breast cancer. This same dense breast tissue that harbors cancers also makes diagnosis and treatment more difficult. Having dense breast tissue is a double-edged sword.

Menstrual cycle

Women who have their first menstrual period early (before age 12) and women who experience menopause late (after the age of 55) have an increased risk of developing and dying from breast cancer. This is thought to be linked to higher levels of the hormones estrogen and progesterone experienced by women who have a longer menstrual life cycle.

Early life radiation exposure

Women who have exposure to radiation in their chest area (usually as treatment for another cancer or disease) have a much higher risk of breast cancer. The risk from chest radiation or radiation exposure is highest if it occurred during a woman’s teen years, when the breasts are still developing.


Women who never have children and women who have their first child after age 30 have a higher risk of developing breast cancer. To that end, women who have been pregnant multiple times or women who get pregnant early in life are at a reduced risk of cancer.

Birth control pills

Recent studies suggest that women who use birth control pills have a greater risk of dying from breast cancer. Luckily, the danger of developing cancer goes away once the birth control pills are stopped. Women should always talk to their doctor about the risks of taking birth control or any other hormone treatment.


Controversial studies in breast-feeding have shown that women who breast-feed for more than a month have a slightly lower risk of developing breast cancer. The longer a woman breast-feeds, the less her chances are of developing breast cancer.

Use of alcohol

Consuming alcohol increases the risk of breast cancer. The amount of alcohol consumed does affect the risk, as women who have seven drinks a week or less don’t really face a greater chance of breast cancer, while as few as ten drinks a week can increase your risk of cancer. The American Cancer Society now suggests that women limit their alcohol intake to seven drinks per week or less.


Being significantly overweight or obese is clearly linked to a higher risk of breast cancer. This is especially true for women after menopause or for women whose weight gain happened during adulthood. “Belly fat”, or weight around the waist, appears to be the most dangerous type of weight for breast cancer development.

Not exercising

We know that regular exercise reduces incidents of breast cancer. The amount of exercise needed to lower your risk is unknown–one research team found that as little as an hour of exercise per week can reduce your risk, while another study suggested two or three periods of cardio exercise are required. The American Cancer Society says that exercising for 45 to 60 minutes four or more days a week is the best way to lower your cancer risk.


You may have seen a popular chain e-mail rumor that says that underarm deodorant causes breast cancer. There is little to no evidence to support the claim, and in fact, large studies of breast cancer show that there is no higher incidence of breast cancer in women who use deodorant.


Similar to the ridiculous antiperspirant rumor above, there’s an e-mail floating around that suggests that wearing a bra (or wearing a bra that is too small) contributes to breast cancer. This has been proven false, and there’s no medical evidence to suggest that any type of clothing can contribute to developing breast cancer.


Wild rumors about how breast cancer develops are plentiful. The claim that abortion increases breast cancer risk is one of these wild rumors, and has been proven false. The same is true for miscarriage–there’s no evidence that terminating a pregnancy either through abortion or miscarriage increases the risk of breast cancer.

Breast implants

While some types of breast implants cause scar tissue to form in the breast tissue, doctors have concluded that the presence of scar tissue does not increase breast cancer risk.

Environmental factors

This is a new area of research–how does our environment affect the rate and development of breasts cancer? It is still unclear, though exposure to substances like certain plastics, some cosmetics and hair care products, and even pesticides is known to be medically harmful. A link between pollution and breast cancer has not yet been established.


Strangely enough, no medical study has yet proven a link between cigarette smoking and breast cancer. Tobacco smoke may cause other cancers to develop, but its impact on the development of breast cancer has not yet been proven.

The night shift

Some medical studies have shown a link between working overnight and the development of breast cancer. This effect was first seen in nurses who work the night shift, who were found to develop breast cancer at a much higher rate. The medicine behind the link is unclear, and more research is required to teach us exactly why this link exists.

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