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In the United States, breast cancer is the most common cancer occurring in women (excluding skin cancer) and the second most common cause of death from cancer in women, after lung cancer. Men can also develop breast cancer, but male breast cancer is rare, accounting for less than 1% of all breast cancer cases. Cancer begins when normal cells in the breast begin to change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
The breast is mainly composed of fatty tissue. Within this tissue is a network of lobes, which are made up of tiny, tube-like structures called lobules that contain milk glands. Tiny ducts connect the glands, lobules, and lobes, carrying the milk from the lobes to the nipple, located in the middle of the areola (darker area that surrounds the nipple of the breast). Blood and lymph vessels run throughout the breast; blood nourishes the cells, and the lymph system drains bodily waste products. The lymph vessels connect to lymph nodes, which are tiny, bean-shaped organs that normally help fight infection.
About 90% of all breast cancer cases start in the ducts or lobes. Almost 75% of all breast cancers begin in the cells lining the milk ducts and are called ductal carcinomas. Cancer that begins in the lobules is called lobular carcinoma. If the disease has spread outside of the duct and into the surrounding tissue, it is called invasive or infiltrating ductal carcinoma. If the disease has spread outside of the lobule, it is called invasive or infiltrating lobular carcinoma. Disease that has not spread is called in situ, meaning "in place." The course of in situ disease, as well as its treatment, depends on whether it is ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS).
Currently, oncologists recommend that DCIS, which accounts for the majority of in situ breast cancers, be surgically removed to help prevent the cancer from changing into an invasive breast cancer and potentially spreading to other parts of the breast or the body. In addition to surgery, radiation therapy and hormone therapy may be recommended for DCIS (see Treatment for more information).
LCIS is not considered cancer and is usually monitored by the doctor. LCIS is a risk factor for breast cancer (see the Risk Factors section).
Other, less common cancers of the breast include medullary, mucinous, tubular, metaplastic, and papillary breast cancer. Inflammatory breast cancer is a faster-growing type of cancer that accounts for about 1% to 5% of all breast cancers. It may be misdiagnosed as a breast infection because there is often swelling of the breast and redness of the breast skin. Paget's disease is a type of in situ cancer that can begin in the ducts of the nipple. The skin often appears scaly and may be itchy.
Cancer may begin as a single, genetically abnormal cell. As this one cell divides, it eventually becomes a tumor and develops a blood supply to nourish its continued growth. At some point, cells may break off from the primary mass and move to other parts of the body in a process called metastasis.
Breast cancer spreads when breast cancer cells move to other sites in the body through the blood vessels and/or lymph vessels. A common site of spread is the regional lymph nodes. The lymph nodes can be axillary (located under the arm), cervical (located in the neck), or supraclavicular (located just above the collarbone). The most common sites of distant metastasis are the bones, lungs, and liver. Less commonly, breast cancer may spread to the brain. The cancer can also recur (come back after treatment) locally in the skin, in the same breast (if it was not removed as part of treatment), other tissues of the chest, or elsewhere in the body.
Most of the time, breast cancer is diagnosed and treated before metastasis occurs. According to the latest data from the National Cancer Institute (NCI), 61% of breast cancers are diagnosed while the cancer is still in the breast, 31% are diagnosed after the cancer has spread to nearby lymph nodes or just outside the breast, and 6% are diagnosed once the cancer has metastasized beyond the adjoining lymph nodes to distant sites.
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In 2009, an estimated 192,370 women in the United States will be diagnosed with invasive breast cancer, and 62,280 women will be diagnosed with in situ breast cancer. An estimated 1,910 men in the United States will be diagnosed with breast cancer. It is estimated that 40,610 deaths (40,170 women, 440 men) from this disease will occur this year.
If the cancer is limited to the breast, the five-year relative survival rate (percentage of people who survive at least five years after the cancer is detected, excluding those who die from other diseases) is 98%. If the cancer has spread to the regional lymph nodes, the five-year relative survival rate is 84%. If the cancer has spread to a distant site, the five-year relative survival rate is 27%. Even if the cancer is found at a more advanced stage, new treatments enable many people with breast cancer to experience the same quality of life as before their diagnosis.
It is important to note that these statistics are averages, and each individual's risk depends upon numerous factors, including the size of the tumor and the number of positive lymph nodes (lymph nodes that contain cancer; this is called "node-positive cancer," see Diagnosis). The survival rate is higher and the chance of recurrence is lower for a smaller tumor with negative lymph nodes (lymph nodes that do not contain cancer; this is called "node-negative cancer"). The recurrence rate increases with an increase in tumor size and number of positive lymph nodes.
Since 1990, the number of women who have died of breast cancer has declined steadily each year. In women younger than 50, there has been a decrease of 3% per year; in women age 50 and older, the decrease has been 2% per year. Currently, there are about two and a half million women living in the United States who have been diagnosed with and treated for breast cancer.
Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States each year, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with breast cancer. Because the survival statistics are measured in five-year intervals, they may not represent advances made in the treatment or diagnosis of this cancer.
Statistics adapted from the American Cancer Society's publication, Cancer Facts & Figures 2009.
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Additional information *
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- Risk Factors
- Staging With Illustrations
- Side Effects
- Questions to Ask the Doctor
- Current Research
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- After Treatment
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