Breast cancer is cancer that forms in the cells of the breasts. There are numerous types of breast cancer, but cancer that begins in the milk ducts (ductal carcinoma) is the most common type.
After skin cancer, breast cancer is the most common cancer diagnosed in women in the United States. Breast cancer can occur in both men and women, but it's far more common in women.
Public support for breast cancer awareness and research funding has helped improve the diagnosis and treatment of breast cancer. Breast cancer survival rates have increased and the number of deaths has been declining, thanks to a number of factors such as earlier detection, new treatments and a better understanding of the disease.
It's not clear what causes breast cancer. Doctors know that breast cancer occurs when some breast cells begin growing abnormally. These cells divide more rapidly than healthy cells do. The accumulating cells form a tumor that may spread (metastasize) through your breast, to your lymph nodes or to other parts of your body.
Breast cancer most often begins with cells in the milk-producing ducts. Doctors call this type of breast cancer invasive ductal carcinoma. Breast cancer may also begin in the milk glands known as lobules (invasive lobular carcinoma) within the breast.
Researchers have identified things that can increase your risk of breast cancer. But it's not clear why some people who have no risk factors develop cancer, yet other people with risk factors never do. It's likely that breast cancer is caused by a complex interaction of your genetic makeup and your environment.
Inherited breast cancer Doctors estimate that only 5 to 10 percent of breast cancers are linked to gene mutations passed through generations of a family. A number of inherited defective genes that can increase the likelihood of breast cancer have been identified. The most common are breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2), both of which increase the risk of both breast and ovarian cancer.
If you have a strong family history of breast cancer or other cancers, blood tests may help identify defective BRCA or other genes that are being passed through your family. Consider asking your doctor for a referral to a genetic counselor, who can review your family health history. A genetic counselor can also discuss the benefits, risks and limitations of genetic testing with you. It's important to remember that the genetic tests help to identify a high-risk individual or family, but they don't definitively predict who will or will not get breast cancer.
Risk factors
A risk factor is anything that makes it more likely you'll get a particular disease. But having one or even several risk factors doesn't necessarily mean you'll develop cancer — many women who develop breast cancer have no known risk factors other than simply being women.
Factors that are associated with an increased risk of breast cancer include:
Being female. Women are much more likely than men are to develop breast cancer.
Increasing age. Your risk of breast cancer increases as you age. Women older than 55 have a greater risk than do younger women.
A personal history of breast cancer. If you've had breast cancer in one breast, you have an increased risk of developing cancer in the other breast.
A family history of breast cancer. If you have a mother, sister or daughter with breast cancer, you have a greater chance of being diagnosed with breast cancer. Still, the majority of people diagnosed with breast cancer have no family history of the disease.
Inherited genes that increase cancer risk. Certain gene mutations that increase the risk of breast cancer can be passed from parents to children. The most common gene mutations are referred to as BRCA1 and BRCA2. These genes can greatly increase your risk of breast cancer and other cancers, but they don't make cancer inevitable.
Radiation exposure. If you received radiation treatments to your chest as a child or young adult, you're more likely to develop breast cancer later in life.
Obesity. Being overweight or obese increases your risk of breast cancer because fat tissue produces estrogen that may help fuel certain cancers.
Beginning your period at a younger age. Beginning your period before age 12 increases your risk of breast cancer.
Beginning menopause at an older age. If you began menopause after age 55, you're more likely to develop breast cancer.
Having your first child at an older age. Women who give birth to their first child after age 35 may have an increased risk of breast cancer.
Postmenopausal hormone therapy. Women who take hormone therapy medications that combine estrogen and progesterone to treat the signs and symptoms of menopause have an increased risk of breast cancer.
Drinking alcohol. Drinking alcohol increases the risk of breast cancer. Experts recommend no more than one alcoholic beverage a day for women.
Other risk factors that have been suggested, but don't play any role in the development of breast cancer include tightfitting bras, antiperspirants, breast implants and shift work.
Chemotherapy Chemotherapy uses drugs to destroy cancer cells. If your cancer has a high chance of returning or spreading to another part of your body, your doctor may recommend chemotherapy to decrease the chance that the cancer will recur. This is known as adjuvant systemic chemotherapy.
Chemotherapy is sometimes given before surgery in women with larger breast tumors. Doctors call this neoadjuvant chemotherapy. The goal is to shrink a tumor to a size that makes it easier to remove with surgery. This may also increase the chance of a cure. Research is ongoing into neoadjuvant chemotherapy to determine who may benefit from this treatment.
Chemotherapy is also used in women whose cancer has already spread to other parts of the body. Chemotherapy may be recommended to try to control the cancer and decrease any symptoms the cancer is causing.
Chemotherapy side effects depend on the drugs you receive. Common side effects include hair loss, nausea, vomiting, fatigue and a small increased risk of developing infection.
Hormone therapy Hormone therapy — perhaps more properly termed hormone-blocking therapy — is often used to treat breast cancers that are sensitive to hormones. Doctors sometimes refer to these cancers as estrogen receptor positive (ER positive) and progesterone receptor positive (PR positive) cancers.
Hormone therapy can be used after surgery or other treatments to decrease the chance of your cancer returning. If the cancer has already spread, hormone therapy may shrink and control it.