Breast cancer is the most common cancer among women, after skin cancer. One in eight women in the United States (roughly 12%) will develop breast cancer in her lifetime. It is also the second leading cause of cancer death in women after lung cancer. Encouragingly, the death rate from breast cancer has declined a bit in recent years, perhaps due to greater awareness and screening for this type of cancer, as well as better treatments.
Breast cancer is a disease that occurs when cells in breast tissue change (or mutate) and keep reproducing. These abnormal cells usually cluster together to form a tumor. A tumor is cancerous (or malignant) when these abnormal cells invade other parts of the breast or when they spread (or metastasize) to other areas of the body through the bloodstream or lymphatic system, a network of vessels and nodes in the body that plays a role in fighting infection.
Breast cancer usually starts in the milk-producing glands of the breast (called lobules) or the tube-shaped ducts that carry milk from the lobules to the nipple. Less often, cancer begins in the fatty and fibrous connective tissue of the breast.
New cases of breast cancer are about 100 times more common in women than in men, but yes, men can get breast cancer too. Male breast cancer is rare, but anyone with breast tissue can develop breast cancer.
What causes breast cancer?
Breast cancer is caused by a genetic mutation in the DNA of breast cancer cells. How or why this damage occurs isn’t entirely understood. Some mutations may develop randomly over time, while others are inherited or may be the result of environmental exposures or lifestyle factors.
Most breast cancers are diagnosed in women over age 50, but it’s not clear why some women get breast cancer (including women with no risk factors) and others do not (including those who do have risk factors).
Some breast cancer risks may be preventable. Of course, you cannot control every variable that may influence your risk. Here are the key breast cancer risk factors to know.
- Age and gender. If you are a woman and you’re getting older, you may be at risk of developing breast cancer. The risk begins to climb after age 40 and is highest for women in their 70s.
- Family history. Having a close blood relative with breast cancer increases your risk of developing the disease. A woman’s breast cancer risk is almost double if she has a mom, sister, or daughter with breast cancer and about triple if she has two or more first-degree relatives with breast cancer.
- A breast cancer gene mutation. Up to 10% of all breast cancers are thought to be inherited, and many of these cases are due to defects in one or more genes, especially the BRCA1 or BRCA2 genes. (Scientists are studying several other gene mutations as well.) In the U.S., BRCA1 and BRCA2 mutations are more common in Jewish women of Eastern European descent. Having these defective genes doesn’t mean you will get breast cancer, but the risk is greater: A woman’s lifetime risk of breast cancer with a BRCA1 gene mutation, for example, may be more like 55% to 65% compared to the average 12%.
- Breast changes and conditions. Women with dense breasts or with a personal history of breast lumps, a previous breast cancer, or certain non-cancerous breast conditions are at greater risk of developing breast cancer than women who do not have these conditions.
- Race/ethnicity. White women are slightly more likely to develop breast cancer than Asian, Hispanic, and African American women. But African American women are more likely to develop more aggressive breast cancer at a younger age and both African American and Hispanic women are more likely to die from breast cancer than white women.
- Hormones. Women with early menstrual periods (starting before age 12) and late menopause (after age 55) are at greater risk of getting breast cancer. Scientists think their longer exposure to the female hormone estrogen may be a factor, because estrogen stimulates growth of the cells of the breast. Likewise, use of hormone therapy after menopause appears to boost the risk of breast cancer. Oral birth control pills have been linked to a small increase in breast cancer risk compared with women who never used hormonal contraception. But that risk is temporary: More than 10 years after stopping the pill, a woman’s breast cancer risk returns to average.
- Weight. Women who are overweight or obese after menopause are more likely to get breast cancer. The exact reason why isn’t clear, but it may be due to higher levels of estrogen produced by fat cells after menopause. Being overweight also boosts blood levels of insulin, which may affect breast cancer risk.
- Alcohol consumption. Studies suggest women who drink two or more alcoholic beverages a day are 1 1/2 times more likely than non-drinkers to develop breast cancer. The risk rises with greater alcohol intake, and alcohol is known to increase the risk of other cancers too. For that reason, the American Cancer Society (ACS) recommends that women stick to one drink a day–or less.
- Radiation exposure. A woman’s risk of developing breast cancer may be higher than normal if she had chest radiation for another disease as a child or young adult.
- Pregnancy history. Having no children or having a first child after age 30 may increase your risk of breast cancer.
- DES exposure. Women who were given the now-banned drug diethylstilbestrol to prevent miscarriage decades ago face a slightly increased risk of breast cancer, as do their daughters.
Scientists are studying a slew of other factors to determine what role, if any, they may play in the development of breast cancer. There’s not enough evidence to say for sure whether smoking, dietary fat, or environmental exposure to certain chemicals, for example, ramp up the risk for breast cancer because study results to date are mixed.