The breasts sit on the chest muscles that cover the ribs. Each breast is made of 15 to 20 lobes. Lobes contain many smaller lobules. Lobules contain groups of tiny glands that can produce milk. Milk flows from the lobules through thin tubes called ducts to the nipple. The nipple is in the center of a dark area of skin called the areola. Fat fills the spaces between the lobules and ducts.
Breast cancer incidence is much higher in industrialised Western countries, whether in Europe or North America, than in developing countries. North American women have the highest incidence of breast cancer in the world. Among women in the U.S., breast cancer is the most common cancer and the second-most common cause of cancer death (after lung cancer). Women in the U.S. have a 1 in 8 (12.5%) lifetime chance of developing invasive breast cancer and a 1 in 35 (3%) chance of breast cancer causing their death. In 2007, breast cancer was expected to cause 40,910 deaths in the U.S. (7% of cancer deaths; almost 2% of all deaths)
Breast cancer is the most common cause of cancer in women and the second most common cause of cancer death in women in the U.S. While the majority of new breast cancers are diagnosed as a result of an abnormality seen on a mammogram, a lump or change in consistency of the breast tissue can also be a warning sign of the disease. Heightened awareness of breast cancer risk in the past decades has led to an increase in the number of women undergoing mammography for screening, leading to detection of cancers in earlier stages and a resultant improvement in survival rates.
Breast cancer is the number one disease that women in the United States fear the most, and for compelling reasons. It is the leading cause of death among women between 40 and 55 years of age and is the second overall cause of death among women (exceeded only by lung cancer). Unfortunately, it is also on the rise worldwide. According to the American Cancer Society, this year about 175,000 new cases of invasive breast cancer and about 43,300 deaths from breast cancer will occur among women in the USA.
Breast cancer is the most common malignancy affecting women in North America and Europe. Close to 200,000 cases of breast cancer were diagnosed in the United States in 2001. Breast cancer is the second leading cause of cancer death in American women behind lung cancer. The lifetime risk of any particular woman getting breast cancer is about 1 in 8 although the lifetime risk of dying from breast cancer is much lower at 1 in 28. Men are also at risk for development of breast cancer, although this risk is much lower than it is for women.
Breast cancer is more easily treated and often curable if it is found early. Monthly breast self-examinations should begin at age 20. Recommended screening methods include breast self-examination and mammography.
The most serious cancers are metastatic cancers. Metastasis means that the cancer has spread from the place where it started into other tissues distant from the original tumor site. The most common place for breast cancer to metastasize is into the lymph nodes under the arm or above the collarbone on the same side as the cancer. Other common sites of breast cancer metastasis are the brain, the bones, and the liver.
Death rates from breast cancer have been gradually declining and continue to decline. These decreases are likely due both to increased awareness and screening and improved treatment methods.