The precise cause of breast cancer is unknown. Most cases of breast cancer occur in women who are not classified as high risk. More research must be done in order to uncover other possible causes.

Genetics: In most cases, it isn't clear what triggers abnormal cell growth in breast tissue, but it is estimated that between 5 and 10% of breast cancers are inherited. Having a mother and/or a sister with the disease increases the risk. About a quarter of breast cancer cases occur in women who have the disease in the family. Defects in one of two genes, breast cancer gene 1 (BRCA1) or breast cancer gene 2 (BRCA2), put an individual at a greater risk of developing both breast and ovarian cancer. Inherited mutations in the ataxia-telangiectasia mutation gene, the cell-cycle checkpoint kinase 2 (CHEK-2) gene and the p53 tumor suppressor gene also make it more likely that an individual will develop breast cancer.

Genetic mutations may result from radiation exposure. Women treated with chest radiation therapy in childhood, for instance, have a significantly higher incidence of breast cancer than women not exposed to radiation. Mutations may also develop as a result of exposure to cancer-causing chemicals, such as the polycyclic aromatic hydrocarbons found in tobacco and charred red meats.

Estrogen: The female hormone estrogen is linked to breast cancer. The role of estrogen and its relation to breast cancer is not yet completely understood. If the individual has never given birth, they are at greater risk for breast cancer because of more exposure to estrogen than women who have had a baby. This is because the body produces less estrogen when one is pregnant. Taking estrogen after menopause (hormone replacement therapy: HRT) also increases the risk. It is important to remember that taking estrogen after menopause also increases the long-term risk of heart disease, uterine cancer, and stroke.

Diet: Some studies suggest that a diet high in animal fat and protein may cause breast cancer, although the results of these studies are not definite.

Others: Other research has focused on certain preservatives (parabens) that are used in deodorants and antiperspirants, as well as many cosmetics, foods, and pharmaceutical products. A study did not show any increased risk for breast cancer in women who reported using an underarm antiperspirant or deodorant. Some chemicals in the environment may mimic estrogen in the body which that may lead to breast cancer.

Early detection remains the best way to prevent debilitation and death from breast cancer. Traditionally, mammography, clinical breast examinations (CBE), and breast self examinations (BSE) have been accepted as legitimate breast screening modalities.

Genetic testing: Women with BRCA1 or BRCA2 (both primary genes involved in breast cancer) genetic mutations may be advised to begin screening at age 25 because of their increased risk for developing breast cancer.

Breast self-examination (BSE): In about 80% of breast cancer cases, the woman detects the lump herself. Women are advised to examine their breasts on a monthly basis starting around age 20. Women may be able to detect early signs of cancer if they become proficient at BSE and familiar with the usual appearance and feel of their breasts. A study did find that women who perform regular breast self-exams might be more likely to undergo unnecessary biopsies after finding breast lumps. Breast self-examination should be performed once a month at the same time each month, one week after a woman's period.

Clinical breast exam (CBE): Unless there is a family history of cancer or other factors that place the individual at high risk, the American Cancer Society recommends having clinical breast exams once every three years until age 40. After that, the American Cancer Society recommends having a yearly CBE. During this exam, the doctor examines the breasts for lumps or other changes. He or she may be able to feel lumps missed by self-examination and will also look for enlarged lymph nodes in the armpit (axillary).

Mammography: Overall mammography is a very effective breast cancer screening tool, and has the ability to detect breast cancers before they can be felt. It may be more effective at detecting tumors in older women than in younger women, and not all cancers can be detected by this method. Images on mammograms appear in gradations of black, gray and white depending on the density of the tissue. Bone shows up as white, fat appears dark gray, and cancerous tumors appear a lighter shade of gray or white.

Unfortunately, dense normal breast tissue can also appear light gray on a mammogram, which can make mammograms harder to interpret in younger women, since they tend to have breast tissue that is denser. After menopause, though, breast density usually begins to decrease, making the mammograms of older women easier to read. For this reason, it is important to follow the guidelines for clinical breast examination (CBE) and to practice regular breast self-examination (BSE).

If a lump in the breast is found, either by breast self-exam or mammography, other tests will be performed in order to make a diagnosis. The only proven way to reduce the risk of dying from breast cancer is by having regular mammograms after the age of 50.

Computer-aided detection (CAD): Radiologists normally view X-rays and mammograms, and their skills and experience play a large part in determining the accuracy of the test results. In CAD, a computer scans the mammogram after a radiologist has reviewed it. CAD identifies more suspicious areas on the mammogram, but many of these areas may later prove to be normal. Using mammography and CAD together may increase the cancer detection rate.

Digital mammography: In this procedure, an electronic process is used to collect and display X-ray images on a computer screen. This allows the radiologist to alter contrast and darkness, making it easier to identify subtle differences in tissue. In addition, the images can be transmitted electronically, so women who live in remote areas can have their mammograms read by an expert who is based elsewhere.

Magnetic resonance imaging (MRI): MRI uses a magnet linked to a computer to take pictures of the interior of the breast. Although not used for routine screening, MRIs can reveal tumors that are too small to detect through physical exams or are difficult to see on conventional mammograms. Some centers may use MRI as an additional screening tool for high-risk women who have dense breast tissue on a mammogram. MRIs aren't recommended for routine screening because they have a high rate of false-positive results, which lead to unnecessary anxiety and biopsies. They are also expensive and not readily available.

Ductal lavage: In this procedure, the doctor inserts a tiny, flexible tube (catheter) into the lining of a duct in the breast and withdraws a sample of cells. The cells are then examined for precancerous changes that might eventually lead to disease. These changes show up long before tumors can be detected on a mammogram. Ductal lavage isn't recommended as a screening tool for high-risk women. It is a new procedure with risks, including the rate of false-negative results and its inability to determine the exact location of abnormal cells and whether they will lead to cancer.

Breast ultrasound (ultrasonography): The doctor may use this technique to evaluate an abnormality seen on a mammogram or found during a clinical exam. Ultrasound uses sound waves to form images of structures deep within the body. Because it doesn't use X-rays, ultrasound is a safe diagnostic tool that can help determine whether an area of concern is a cyst or solid tissue. Breast ultrasound isn't used for routine screening because it has a high rate of false-positive results.

Molecular breast imaging (MBI): This experimental technique tracks the movement of a radioactive isotope that's taken up by breast tissue, particularly the tumors. Images are taken of the breast when the radioactive isotope signals are detected. In preliminary studies, MBI found small tumors that both mammography and ultrasound missed. This procedure uses lighter compression, and may be more comfortable than mammography. The MBI takes about 40 to 50 minutes as opposed to 15 minutes for a mammogram, and the procedure is more invasive due to the injection. It is still unclear how abnormal findings are biopsied, and the studies remain ongoing.

Fine needle aspiration: A thin needle is inserted into the lump and a sample is withdrawn. This test helps to determine if the lump is fluid-filled (a cyst, usually not cancerous) or a solid tumor. It can be performed in a doctor's office with local anesthesia. The sample, regardless if it is fluid or solid, is sent to the laboratory for further analysis.

Core biopsy: A larger needle is inserted into a lump or an abnormal area seen on a mammogram, and the tissue sample is removed. The sample is analyzed for cancer cells, and this procedure is usually performed at a hospital with local anesthesia.

Surgical biopsy: The lump and surrounding tissue is removed surgically before being sent to a laboratory for analysis. This procedure needs to be done in a hospital with either a local or general anesthetic.

Stereotactic biopsy. This technique is used to sample and evaluate an area of concern that can be seen on a mammogram, but cannot be felt or seen on an ultrasound. During the procedure, a radiologist takes a core needle biopsy using the mammogram as a guide. Stereotactic biopsy usually takes about an hour and is performed using local anesthesia.

Wire localization. A doctor may recommend this technique when a worrisome lump is seen on a mammogram, but can't be felt or evaluated with a stereotactic biopsy. Using the mammogram as a guide, a thin wire is placed in the breast and is guided toward the lump. Wire localization is usually performed right before a surgical biopsy, and is a way to help the surgeon find the area to be removed and tested.

Estrogen and progesterone receptor tests: If a biopsy reveals malignant cells, estrogen and progesterone receptor tests are usually performed on the malignant cells. These tests help determine whether female hormones affect the way the cancer grows. If the cancer cells have receptors for estrogen, progesterone or both, the doctor may recommend treatment with a drug tamoxifen, which prevents estrogen from binding to these sites.

Staging: Staging breast cancer is used to help determine the course of treatment and the prognosis. Staging is based on the size of the tumor, how much of the breast tissue is cancerous, whether the underarm (axillary) lymph nodes are also cancerous, and whether cancer can be found in other parts of the body. The five-year survival rate for localized breast cancer (not spread to the axillary lymph nodes) is 96%. If cancer has spread regionally, the rate is 77%. For those women who are diagnosed with metastatic disease, the five-year survival rate is only 5 to 10%. Stage 0 cancers are also called noninvasive, or in situ (in one place) cancers. Stage I to IV cancers are invasive tumors that have the ability to spread to other areas.

Common signs and symptoms of breast cancer include a lump in the breast that feels distinctly different from other breast tissue or that does not go away, swelling of the breast that does not go away, thickening of breast tissue, dimpling or pulling of the skin on the breast which may then resemble the skin of an orange, any change in the breast shape or contour, nipple discharge, retraction of the nipple, scaliness of the nipple, pain or tenderness of the breast, and swollen bumps or puss-filled sores.

Fibrocystic changes: This condition can cause the breasts to feel ropy or granular. Fibrocystic changes are extremely common, occurring in at least half of all women. In most cases the changes are harmless. If the breasts are very lumpy, then performing a breast self-exam is more challenging.

Cysts: These are fluid-filled sacs that frequently occur in the breasts of women ages 35 to 50. Cysts can range from very tiny to about the size of an egg. They can increase in size or become more tender just prior to menstruation, and may disappear completely after. Cysts are less common in postmenopausal women.

Fibroadenomas: These are solid, noncancerous tumors that often occur in women during their reproductive years. A fibroadenoma is a firm, smooth, rubbery lump with a well-defined shape. It will move under the skin when touched, and is usually painless. Over time, fibroadenomas may grow larger, smaller or even disappear completely.

Infections: Breast infections (mastitis) are common in women who are breastfeeding or who have recently stopped breastfeeding, but mastitis may develop when women are not nursing. The breast will likely be red, warm, tender and lumpy, and the lymph nodes under the arm may swell. The individual may also feel slightly ill and present with a low-grade fever.

Trauma: Sometimes a blow to the breast or a bruise also can cause a lump, but this doesn't mean the individual is more likely to get breast cancer.

Calcium deposits (microcalcifications): These tiny deposits of calcium can appear anywhere in the breast and often show up on a mammogram. Most women have one or more areas of microcalcifications of various sizes. They may be caused by secretions from cells, cellular debris, inflammation, trauma or prior radiation. Calcium deposits are not the result of taking calcium supplements. The majority of calcium deposits are harmless, but a small percentage may be precancerous or cancer.

Inflammatory breast cancer (IBC): Symptoms of IBC can include one breast larger than the other, red or pink skin, swelling, rash (entire breast or small patches), orange-like texture (peau d' orange), skin hot to the touch, pain and/or itchiness, ridges or thickened areas of breast, nipple discharge, nipples that appear inverted or flattened, swollen lymph nodes under the armpit, and sometimes swollen lymph nodes of the neck.

Complications of breast cancer include depression, loss of sexual interest, cachexia (physical weakness, muscle loss, and weight loss), cerebral metastases (brain), lymphangitis carcinomatosa (inflammation of the lymph vessels secondary to cancer), breast lumps, opsoclonus (uncontrolled eye movement), lung metastases, brachial plexus neuropathy (nerve damage), back pain, liver metastases, bone metastases, prostate specific antigen levels raised (plasma or serum in men), bone pain, CEA raised (marker for colon cancer), renal metastases (kidney), mastalgia (breast pain), pleural effusion (fluid around the lungs), lymphadenopathy (swelling of the lymph nodes), leucoerythroblastic anemia (blood condition), cutaneous metastasis (skin), osteosclerosis (abnormal hardness and density of the bone), and nipple discharge.

Age: The chances of developing breast cancer increases with age. The disease rarely affects women younger than 25 years of age, whereas close to 80% of breast cancers occur in women older than age 50. At age 40, there is a one in 252 chance of developing breast cancer. By age 85, the chances are one in eight.

A personal history of breast cancer: If an individual has had breast cancer in one breast, there is an increased risk of developing cancer in the other breast.

Family history: If the individual's mother, sister, daughter or male relative has had breast cancer, ovarian cancer, or both, the risk of developing breast cancer is doubled. In general, the more relatives one has with breast cancer that were premenopausal at the time of diagnosis, the higher the risk.

Genetic predisposition: Between 5 and 10% of breast cancers are inherited. Defects in one of several genes, especially BRCA1 or BRCA2, put the individual at a greater risk for developing breast, ovarian and colon cancers. Usually these genes help prevent cancer by making proteins that keep cells from growing abnormally, but if they are mutated, then the genes aren't effective at protecting the individual from cancer.

Radiation exposure: Radiation treatments to the chest experienced as a child or young adult may increase in the risk of developing breast cancer later in life. The younger the individual was when they received the treatments the greater the risk.

Excess weight: The relationship between excess weight and breast cancer is complex. In general, weighing more than what is normal for the patient's age and height increases the risk of breast cancer, especially if the patient has gained the weight as an adult or in postmenopause. The risk is even greater if the excess fat is in the upper part of the body. Although women usually have more fat in their thighs and buttocks, they tend to gain weight in their abdomens in their 30s, which can increase their risk of developing breast cancer.

Exposure to estrogen: The longer an individual is exposed to estrogen, the greater the risk of breast cancer. In general, if an individual has a late menopause (after age 55) or early menses (before age 12), there is a slightly higher risk of developing breast cancer. Women who never had children or whose first pregnancy occurred when they were age 35 or older also have an increased risk of developing breast cancer.

Race: Caucasian women are more likely to develop breast cancer than African-American or Hispanic women. However, African-American women are more likely to die of the disease because their cancers are found at a more advanced stage. Although some studies show that African-American women may have more aggressive tumors, socioeconomic factors may enter the picture also. Women of all races with incomes below the poverty level are often diagnosed with late-stage breast cancer, and are more likely to die of the disease than women with higher incomes. Low-income women don't usually receive the routine medical care that would allow breast cancer to be discovered earlier.

Hormone therapy: A study sponsored by the National Institutes of Health (NIH) in June 2002 was halted as researchers reported that hormone therapy, once considered standard treatment for menopausal symptoms, actually posed more health risks than benefits. Along with an increase in cardiovascular disease and uterine cancer, there was a slightly higher risk of breast cancer for women taking the particular combination of hormone therapy (estrogen plus progestin) used in the study. In addition, combination hormone therapy can make malignant tumors harder to detect on mammograms, leading to cancers that are diagnosed at more advanced stages when they're more difficult to treat.

Birth control pills: The hormone therapy studies have raised questions about the relationship between birth control pills and breast cancer. Studies have reported that women who are currently using birth control or have used them in the past 10 years are at a slightly increased risk for having breast cancer in the next 10 years. These cancers tend to be localized to the breast and are less clinically advanced than the cancers diagnosed in women who never used birth control pills.

Smoking: Studies have found that smoking does increase the incidence of breast cancer in those with the genetic predisposition. More than 30 carcinogenic chemicals are present in tobacco smoke; many of which are fat-soluble, resistant to metabolism and can be stored in breast adipose tissue. A study published in 2001 found that smoking significantly increases the risk of breast cancer in women with a family history of breast and ovarian cancers. A more recent study found that exposure to secondhand smoke also increases the risk of breast cancer in premenopausal women. Researchers hypothesize that higher estrogen levels combined with the cancer-causing agents in tobacco spark the development of breast tumors.

Other carcinogens: Polycyclic aromatic hydrocarbons are chemicals found mainly in cigarette smoke and charred red meat. Studies have shown that exposure to these chemicals can significantly increases the chances of developing breast cancer. Exposure to certain pesticides may also increase the risk.

Excessive use of alcohol: Women who consume more than one alcoholic drink a day have about a 20% greater risk of breast cancer than women who don't drink. The National Cancer Institute recommends limiting alcohol intake to no more than one drink per day.

Precancerous breast changes (atypical hyperplasia, carcinoma in situ ): These changes are often discovered only after a breast biopsy is performed, and they can double the risk of developing breast cancer.