Breast cancer occurs when cells in the breast become abnormal and divide uncontrollably. Breast cancer usually starts in the glands that produce milk (lobules) or the tubes (ducts) that carry milk from the glands to the nipple.
Among women, breast cancer is the most common cancer and the second most common cause of cancer deaths.
Typically, the first symptom is a painless lump, usually noticed by the woman.
Breast cancer screening recommendations vary and include periodic mammography, breast examination by a doctor, and breast self-examination.
If a solid lump is detected, doctors use a hollow needle to remove a sample of tissue or make an incision and remove part or all of the lump and then examine the tissue under a microscope (biopsy).
Breast cancer almost always requires surgery, sometimes with radiation therapy, chemotherapy, other drugs, or a combination.
Outcome is hard to predict and depends partly on the characteristics and spread of the cancer.
The Breasts
Breast disorders may be noncancerous (benign) or cancerous (malignant). Most are noncancerous and not life threatening. Often, they do not require treatment. In contrast, breast cancer can mean loss of a breast or of life. Thus, for many women, breast cancer is their worst fear. However, potential problems can often be detected early when women do both of the following:
Are examined regularly by their doctor
Have mammograms as recommended
Women should be familiar with how their breasts normally look and feel, and men should also be aware of changes in or around their nipples. If a woman notices a change, she may want to do a breast self-examination. Women should report any changes to a health care practitioner right away. Most medical organizations no longer recommend that people do monthly or weekly breast self-examinations as a routine way to check for cancer. Doing these examinations when there is no lump or other change does not help detect breast cancer early in women who get screening mammograms.
Early detection of breast cancer can be essential to successful treatment.
Breast cancer is the most common cancer among women and, of cancers, is the most common cause of death among Hispanic women and the second most common cause of death in women of other races (after lung cancer). In 2021 in the United States, the following occurred in women:
Invasive breast cancer was diagnosed in about 281,550 women.
Noninvasive (in situ) breast cancer was diagnosed in almost 49,290 women.
Almost 43,600 women died of breast cancer.
Breast cancers in men account for about 1% of all breast cancers. In 2021, 2,650 new cases of invasive breast cancer and 530 deaths from it occurred in men in the United States.
Many women fear breast cancer, partly because it is common. However, some of the fear about breast cancer is based on misunderstanding. For example, the statement, “One of every eight women will get breast cancer,” is misleading. That figure is an estimate of the risk of developing breast cancer during a woman''s life. It means that theoretically, one of eight women will develop breast cancer during her life. However, a 40-year-old woman has only about a 1 in 70 chance of developing it during the next decade. But as she ages, her risk increases.
Table
What Are the Risks of Developing Breast Cancer?
Risk Factors for Breast Cancer
Several factors affect the risk of developing breast cancer. Thus, for some women, the risk is much higher or lower than average. Most factors that increase risk, such as age and certain abnormal genes, cannot be modified. However, regular exercise, particularly during adolescence and young adulthood, may reduce the risk of developing breast cancer.
Far more important than trying to modify risk factors is being vigilant about detecting breast cancer so that it can be diagnosed and treated early, when it is more likely to be cured. Early detection is more likely when women have mammograms. Regular breast self-examinations are also recommended by some doctors, although these examinations have not been shown to reduce risk of death from breast cancer.
Age
Increasing age is the most important risk factor for breast cancer. Most breast cancers occur in women older than 50. Risk is greatest after age 75.
Previous history of breast cancer
Having had breast cancer increases the risk of breast cancer. After the diseased breast is removed, the risk of developing cancer in the remaining breast is about 0.5 to 1.0% each year.
Family history of breast cancer
Breast cancer in a first-degree relative (mother, sister, or daughter) increases a woman’s risk by 2 to 3 times, but breast cancer in more distant relatives (grandmother, aunt, or cousin) increases the risk only slightly. Breast cancer in two or more first-degree relatives increases a woman’s risk by 5 to 6 times.
Breast cancer gene mutation
Mutations in two separate genes for breast cancer (BRCA1 and BRCA2) have been identified. Fewer than 1% of women have these gene mutations. About 5 to 10% of women with breast cancer have one of these gene mutations. If a woman has one of these mutations, her lifetime risk of developing breast cancer is about 50 to 85%. The risk of developing breast cancer by age 80 is about 72% with a BRCA1 mutation and about 69% with a BRCA2 mutation. However, if such a woman develops breast cancer, her chances of dying of breast cancer are not necessarily greater than those of any other woman with breast cancer.
These mutations are most common among Ashkenazi Jews.
Women likely to have one of these mutations are those who have at least two close, usually first-degree relatives who have had breast or ovarian cancer. For this reason, routine screening for these mutations does not appear necessary, except in women who have such a family history.
Having a BRCA mutation also increases the risk of ovarian cancer. During their life, women with BRCA1 gene mutations have about a 40% risk of developing ovarian cancer. For women with BRCA2 gene mutations, risk is about 15%.
Men who have a BRCA gene mutation have a 1 to 2% lifetime risk of developing breast cancer.
Women with one of these mutations need to be tested monitored more closely for breast cancer—for example, by more frequent testing or being screened with both mammography and magnetic resonance imaging (MRI). Or they may need to try to prevent cancer from developing by taking tamoxifen or raloxifene (which is similar to tamoxifen) or sometimes by even having both breasts removed (double mastectomy).
Certain benign changes in the breast
Some changes in the breast seem to slightly increase the risk of breast cancer. They include
Changes in the breast that required a biopsy to rule out cancer
Conditions that change the structure, increase the number of cells, or cause lumps or other abnormalities in breast tissue, such as complex fibroadenoma, hyperplasia (abnormally increased growth of tissue), atypical hyperplasia (hyperplasia with abnormal tissue structure) in the milk ducts or milk-producing glands, sclerosing adenosis (increased growth of tissue in the milk-producing glands), or papilloma (a noncancerous tumor with fingerlike projections)
Dense breast tissue seen on a mammogram
Having dense breast tissue also makes it harder for doctors to identify breast cancer. Having dense breasts means that women have more fibroglandular tissue (composed of fibrous connective tissue and glands) and less fatty tissue in the breast.
For women with such changes, the risk of breast cancer is increased only slightly unless abnormal tissue structure is detected during a biopsy or they have a family history of breast cancer.
Age at first menstrual period, first pregnancy, and menopause
The earlier menstruation begins (especially before age 12), the higher the risk of developing breast cancer.
The later the first pregnancy occurs and the later menopause occurs, the higher the risk. Never having had a baby increases the risk of developing breast cancer. However, women who have their first pregnancy after age 30 are at higher risk than those who never have a baby.
These factors probably increase risk because they involve longer exposure to estrogen, which stimulates the growth of certain cancers. (Pregnancy, although it results in high estrogen levels, may reduce the risk of breast cancer.)
Oral contraceptives or hormonal therapy
Some studies show that women taking oral contraceptives (birth control pills) have a slightly higher risk of breast cancer. Once the pills are stopped, this risk seems to go back to normal within about 10 years.
After menopause, taking combination hormone therapy (estrogen with a progestin) for a few years or more increases the risk of breast cancer. Taking estrogen alone does not appear to increase the risk of breast cancer.
Diet and obesity
Diet may contribute to the development or growth of breast cancers, but evidence about the effect of a particular diet (such as a high-fat diet) is lacking (see also Diet and Cancer).
Risk of developing breast cancer is somewhat higher for women who are obese after menopause. Fat cells produce estrogen, possibly contributing to the increased risk. However, there is no proof that a high-fat diet contributes to the development of breast cancer or that changing the diet can decrease risk. Some studies suggest that obese women who are still menstruating are less likely to develop breast cancer.
Research about the link between obesity and cancer is ongoing (see also the National Cancer Institute: Uncovering the Mechanisms Linking Obesity and Cancer Risk).
Lifestyle
Smoking and regularly drinking alcoholic beverages may increase the risk of breast cancer. Experts recommend that women limit themselves to one alcoholic drink a day. One drink is about 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of more concentrated liquor, such as whiskey.
Radiation exposure
Radiation exposure (such as radiation therapy for cancer or significant exposure to x-rays) before age 30 increases risk.
Types of Breast Cancer
Breast cancer is usually classified by the following
The kind of tissue in which the cancer starts
The extent of the cancer''s spread
The type of tumor receptors on the cancer cells
Kind of tissue
There are many different kinds of tissue in the breast. Cancer can develop in most of these tissues, including
Milk ducts (called ductal carcinoma)
Milk-producing glands, or lobules (called lobular carcinoma)
Fatty or connection tissue (called sarcoma): This type is rare.
Ductal carcinoma accounts for about 90% of all breast cancers.
Paget disease of the nipple is a ductal breast carcinoma that affects the skin over and around the nipple. The first symptom is a crusty or scaly nipple sore or a discharge from the nipple. About half of the women who have this cancer also have a lump in the breast that can be felt. Women with Paget disease of the nipple may also have another breast cancer that is not felt but that can be seen using imaging tests—mammography, magnetic resonance imaging (MRI), or ultrasonography—done to look for another cancer. Because this disease usually causes little discomfort, women may ignore it for a year or more before seeing a doctor. The prognosis depends on how invasive and how large the cancer is as well as whether it has spread to the lymph nodes.
Phyllodes breast tumors are relatively rare, accounting for fewer than 1% of breast cancers. About 10 to 25% are cancerous. They originate in breast tissue around milk ducts and milk-producing glands. The tumor spreads to other parts of the body (metastasizes) in about 10 to 20% of women who have it. It recurs in the breast in about 20 to 35% of women who have had it. The prognosis is
