Breast Cancer, malignant tumor in the glandular tissues of the breast. Such tumors, also called carcinomas, form when the processes that control normal cell growth break down, enabling a single abnormal cell to multiply at a rapid rate (see Cancer). Carcinomas, which tend to destroy an increasing proportion of normal breast tissue over time, may spread, or metastasize, to other parts of the body. Mammogram Mammography is a special X-ray technique that is used to visualize soft tissues of the breast as a means for screening women for breast cancer. This mammogram shows calcification (dense white flecks) in a cancerous tumor. The nipple is to the left. The majority of breast cancers originate in the duct of the mammary, or milk-secreting, gland. The remainder arise in the glands themselves. Most tumors of either type show early evidence of invasive (malignant) behavior, but both may also exist in noninvasive forms.Photo Researchers, Inc./Kings College Hospital/Science Source Breast cancer is the most common cancer in women, other than skin cancer. A major health problem in many parts of the world, it is especially prevalent in developed countries. As a result of large-scale screening of women considered at higher risk, a greater number of breast cancers have been discovered and treated in recent years, even in cases where the women experienced no symptoms. The American Cancer Society (ACS) estimates that in the United States about 203,500 new cases are diagnosed and about 40,000 women die each year from cancer originating in the breast. One in 8 American women who live to age 85 will develop this illness at some time during her life. According to the Canadian Cancer Society, 19,000 new cases are diagnosed in Canada each year, and 5,300 Canadian women die from the disease annually. The rate of incidence increases with age, and women 75 years and older are at highest risk. Breast cancer can affect males, but the disease strikes women about 100 times as often as it does men.
RISK FACTORS
Scientists do not understand exactly what causes breast cancer. Studies suggest that several categories of women are at increased risk for the disease: those with a long menstrual history (menstrual periods that started before age 12 and ended after age 50); those who never gave birth or who waited until after age 30 to have children; and those who have used birth control pills or hormone replacement therapy. Such risk factors, all of which relate to hormone-based life events, suggest that breast cancer is somehow affected by prolonged exposure to female sex hormones, such as estrogen. Women with a history of breast cancer in the family are also at greater risk. About 5 percent of all breast cancers have been attributed to a mutated, or structurally altered, gene known as BRCA1. Mutations in a second gene, BRCA2, contribute significantly to the development of breast cancer in Jewish women of eastern and central European origin. Breast cancer seems to be more common in women who do not exercise regularly and are unable to maintain a healthy body weight. Alcohol has also been linked to increased risk for breast cancer. The ACS reports that women who drink two to five alcoholic beverages a day have about 1.5 times the risk of developing breast cancer than women who drink no alcohol. Studies also indicate that women who routinely work night shifts may increase their risk of developing breast cancer by as much as 60 percent. Scientists theorize that the body’s production of melatonin (a hormone that, among other tasks, regulates sex hormones) peaks during nighttime darkness. Exposure to bright light during the night decreases melatonin production, which may in turn increase estrogen levels. These studies may account for why women in industrialized nations, who are exposed to more artificial light at night, have a greater risk of breast cancer than those in developing nations.
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