Breast cancer is most common in women, though it can occur in anyone with breast tissue. About 1 of every 8 women will develop breast cancer in her lifetime. By contrast, only about 1 man in 1,000 will develop invasive breast cancer in his lifetime. (1)
Breast cancer starts with a tumor in the breast. A tumor is a mass of abnormal cells that rapidly divide and grow. Most tumors begin in either the lobules (the glands that produce milk) or in the ducts (the tubes that bring milk to the nipple). Though it is less common, a tumor can also begin in the connective tissue of the breast.
Risk Factors for Breast Cancer
The largest risk factor for breast cancer is simply being a woman: An estimated 12 percent of women who have an average risk of breast cancer will develop it at some point in their lifetimes. A variety of factors can increase that risk.
Age The risk of breast cancer increases as women age, particularly after age 50 and between ages 60 and 69. Approximately two-thirds of all invasive breast cancer occurs in women at least 55 years old. (2) Half of all cases are diagnosed after age 62. (3)
Family and Personal History Your risk of breast cancer increases if you have close relatives with a breast cancer diagnosis. The risk is twice as high if your mother, sister, or daughter has been diagnosed with breast cancer. If you have a personal history of breast cancer, your risk of developing a new breast cancer is 3 to 4 times greater, aside from any risk of the previous cancer returning. (2)
Genetics Women also have a substantially increased risk of breast cancer if they carry a mutation in one of two genes called BRCA, which are known to be linked to breast and ovarian cancer. There are other genes that increase risk, as well, though they carry significantly less risk than the BRCA mutations.
History of Radiation Past radiation to treat a previous cancer outside of the breast or to treat acne in adolescence increases your lifetime risk of breast cancer.
History of Diethylstilbestrol (DES) Use Women who took DES, a drug that was prescribed between 1938 and 1971 to help sustain pregnancies, have a higher risk of breast cancer. Those exposed to prenatal DES may also be at a higher risk.
Increased Weight Women have a higher risk of breast cancer if they are overweight or obese, particularly after menopause. The risk of recurrence (the cancer coming back) is also higher in overweight women.
Pregnancy and Breast-Feeding History Women have a slightly higher risk of breast cancer if they do not have a full-term pregnancy before age 30. However, breast-feeding reduces the risk of breast cancer, especially if done for a year or longer. (2)
Menstrual History Women’s risk of breast cancer is higher later in life if they got their first period before age 12 or did not enter menopause until after age 55. (2)
Use of Hormone Replacement Therapy These drugs increase the risk of breast cancer.
Drinking Alcohol Beer, wine, and liquor all raise the risk of hormone-receptor-positive breast cancer. (2)
Dense Breasts Women with dense breasts may have up to 6 times greater risk of breast cancer. Mammograms may not detect breast cancer as easily on dense breasts. (2)
Insufficient Physical Activity Women who don’t engage in regular physical exercise are at an increased risk. (2)
Smoking Tobacco use increases the risk of breast cancer when women are younger and premenopausal. Though the research is not certain, regular exposure to very heavy secondhand smoke may increase postmenopausal women’s risk of breast cancer.
Race and Ethnicity White women have a slightly higher risk of breast cancer, followed closely by black women, compared with Latina, Native American or Alaska Native, and Asian or Pacific Islander women. (3) Among women under 45 years old, black women have the highest risk of breast cancer and tend to develop more aggressive, advanced cancer than other diagnosed women under age 50. Black women are also more likely to die from breast cancer than women of other races or ethnicities, due at least in part to unequal access to care. (4)
Environmental Factors Scientists are continuing to explore other possible risk factors that have weak or mixed findings in research. These include a low vitamin D level, light exposure at night (such as from shift work), and an unhealthy diet. (2)
Breast cancer may also be linked to various chemical compounds in cosmetics, food, lawn care products, plastic, sunscreen, water, and grilled meats. (2) Many of these chemicals are not avoidable, and it would take very high exposure over a long time for these chemicals to affect breast cancer risk. Research is unclear on how much or how little these compounds may increase risk.
The BRCA Genes and Beyond: Inherited Risk for Breast Cancer
Women with inherited mutations in the BRCA1 or BRCA2 genes have a higher risk of breast and ovarian cancer than the general population.
About 5 to 10 percent of breast cancer occurs in people with a BRCA gene mutation. (5) About 72 percent of women with a BRCA1 mutation and 69 percent of women with a BRCA2 mutation develop breast cancer before they are 80 years old. Without a BRCA mutation, about 12 percent of women develop breast cancer in their lifetime. (6)
A blood test can analyze your DNA to determine whether you have mutations in either BRCA gene. However, only women with a personal or family history of breast or ovarian cancer, or those of Ashkenazi Jewish ancestry, usually undergo testing. (5)
If you have an average risk of breast or ovarian cancer, it is not typical to get tested for BRCA mutations, and your insurance company is unlikely to cover the cost. However, some private companies offer BRCA gene testing to anyone willing to pay out of pocket. (6)
If you decide to get tested for a BRCA gene mutation, you should seek genetic counseling as well. A counselor can help you understand your test results and your options after you receive them.
Over the years, researchers have identified other inherited genetic mutations that can raise risk, including ATM, PALB2, and TP53, among others.
Breast Cancer: The Signs and Symptoms to Look Out For
The symptoms of breast cancer vary widely among different women but usually involve some kind of change in the breast. (7) Some women may never experience symptoms, but mammography detects the cancer.
The following signs are reasons to contact your provider for a visit:
- Changes in how your breast or nipple feels (7)
- Any lump in or near the breast or underarm
- A hardening, thickening, or swelling area in the breast
- Nipple tenderness without another cause
- Skin dimpling on your breast or enlarged pores that make your breast look similar to an orange peel
- Warmth or unexplained tenderness in the breast
- Irritated or itchy breasts without explanation
The changes in the way your breast or nipple looks (7) can include a variety of differences:
- Any unexplained change in the color, texture, size, or shape of the breasts or nipples
- Unexplained shrinkage of the breast, particularly if only on one side
- A change in how symmetrical your breasts are (if one becomes particularly larger or smaller or differently shaped than the other)
- Nipples that turn inward without explanation
- Scaly, red, or swollen breasts or nipples, including the areola (the darker skin around your nipple)
Any discharge from your nipple that is not breast milk, especially if the discharge is clear or bloody, could be a symptom of breast cancer.
Symptoms of Paget’s Disease
Paget’s disease is a rare type of breast cancer that begins in the nipple and spreads to the areola, the darker skin surrounding the nipple. It makes up less than 5 percent of all breast cancer diagnoses in the United States. (8)
Paget’s disease usually occurs in women who have already had invasive breast cancer or ductal carcinoma in situ (when cancer has developed in the milk ducts but has not spread further). It rarely occurs on its own or in women under 50 years old. (8)
Symptoms typically occur only on one nipple but may come and go over several months. They include the following signs: (9)
- Flaky, scaly, crusty, hardened, irritated, or oozing skin on the nipple or areola
- Itching, tingling, or burning in the nipple or areola
- A yellowish or bloody discharge from the nipple
- A flattened or inverted nipple
- Thickened or scaly skin on the breast
- Painful or especially sensitive nipples
Symptoms of Inflammatory Breast Cancer
Inflammatory breast cancer (IBC) is especially aggressive and grows quickly. However, it often does not cause a lump or show up on a mammogram.
IBC occurs more often in younger women and women who are obese or overweight. Black women may have a higher risk of IBC than women of another race or ethnicity. (10)
IBC symptoms include frequent itching or irritation of the breast, a small rash that might resemble an insect bite, flattened or inverted nipples, or skin changes that look like an orange peel. (11)
The breast often swells and may appear reddish or purplish or even look bruised. At least a third of the breast may feel warmer or heavier than the other. Your breast may feel tender, itchy, or burning. (12)