Overview of Breast Cancer
The cells of our bodies normally grow and divide in an orderly, highly controlled way governed by multiple genes contained within each cell. Cancer occurs when mutations, or abnormal changes, occur in the genes which control cell growth and division. Mutated cells grow and multiply in an uncontrolled disorganized way, forming a tumor. Although breast cancer is always caused by genetic abnormalities, only
5-10% of these genetic alterations are inherited from ones mother or father. 90-95% of breast cancers are due to genetic abnormalities that happen as a result of hormonal, environmental and/or other acquired factors. Multiple genetic hits must occur for a cancer cell to develop.
Breast tissue is composed of glandular tissue, the ducts and lobules, with intervening stroma or supporting tissue comprised of connective and fatty tissue containing blood vessels and lymphatic channels. Breast cancer most commonly originates in the cells lining the breast ducts, which are tubular, branching structures which transport milk from the lobules to the nipple. Less commonly, breast cancer can arise from the cells lining the lobules, the glandular tissue capable of producing milk. When the cancer cells are confined to the ducts, the cancer is carcinoma in-situ. These in-situ or non-invasive cancers have a < 2% chance of metastasizing (spreading) to other parts of the body. Some cancers develop the ability to grow through the membrane of the ducts or lobules and microscopically invade into the stroma. These are invasive or infiltrating carcinoma. Once the breast cancer cells invade the stroma where lymphatic channels and blood vessels are, the cancer can spread (metastasize) to the lymph nodes in the under- arm (via the lymphatic channels) or to other organs (via the blood vessels). The most common sites for distant metastasis are bone, liver, lung or brain. Breast cancer can also spread by growing directly into surrounding structures such as the
skin, chest wall, or muscles. Most breast cancers are detected at early stages when they are confined to the breast with or without involvement of the lymph nodes in the underarm (axillary lymph nodes).
Breast cancer is the most common form of cancer in women in the United States (excepting non-melanoma skin cancer). Slightly less than 30% of cancers in women are breast cancers.
Fortunately, breast cancer incidence has been steadily decreasing from its peak in 1999. Breast cancer mortality, the death rate, has been dropping by 2% per year since 1990. The 5 year survival for breast cancer has increased to 90%, and is 98% for women with cancer only in the breast and not the lymph nodes.
The lifetime risk for breast cancer in US women is 1 in 8 (about 12%). In 2013, it is estimated that 232,340 new cases of invasive breast cancer and 64,640 new cases ofnon-invasive (in situ) breast cancer will be diagnosed in US women.
From 2000 to 2009, the incidence of breast cancer decreased by 0.9% per year among US women. The decrease was seen only in women > 50, at least in part because fewer women were using hormone replacement therapy (HRT) after the Womens Health Initiative study, published in 2002, suggested a link between HRT and breast cancer risk.
Breast cancer is second only to lung cancer in cancer-related deaths (mortality) in US women. Approximately 39,620 women in the U.S. will die from breast cancer in 2013. Breast cancer mortality has been decreasing since 1990, particularly in women under 50. From 2000 to 2009, breast cancer deaths decreased by 2.1% per year in US women. These decreases are thought to be related to earlier detection through screening, and more effective treatments.
A US mans lifetime risk for breast cancer is about 1 in 1,000. About 2,240 new cases of invasive breast cancer are expected in men in 2013 and 410 male breast cancer deaths.
In 2011, there were more than 2.6 million breast cancer survivors in the United States.