Cancer is a group of many related diseases that begin in cells, the body's basic unit of life. The body is made up of many types of cells, and normally, cells grow and divide to produce more cells only when the body needs them. Sometimes, however, cells keep dividing when new cells are not needed. These extra cells form a mass of tissue, called a growth or tumor. There are two types of tumor: benign and malignant.
Benign tumors are not cancer. They can usually be removed, and, in most cases, they do not come back. Cells from benign tumors do not spread to other parts of the body, and are not a threat to life.
Malignant tumors are cancer. Cells in these tumors are abnormal; they divide without control or order, and can invade and damage nearby tissues and organs. Cancer cells can break away from a malignant tumor and enter the bloodstream or the lymphatic system, which is how cancer spreads from the original cancer site to form new tumors in other organs. The spread of cancer is called metastasis.
When cancer arises in breast tissue and spreads outside the breast, cancer cells are often found in the lymph nodes under the arm. If the cancer has reached these nodes, it means that cancer cells may have spread to other parts of the body, including other lymph nodes and other organs, such as the bones, liver, or lungs. When cancer spreads from its original location to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if breast cancer spreads to the brain, the cancer cells in the brain are actually breast cancer cells. The disease is called metastatic breast cancer.
What causes Breast Cancer?
The exact causes of breast cancer are not known. However, studies show that the risk of breast cancer increases with age. The disease is very uncommon in women under the age of 35. Most breast cancers occur in women over the age of 50, and the risk is especially high for women over age 60. Breast cancer occurs more often in white women than African-American or Asian women.
Women with the following conditions have an increased risk for breast cancer:
Personal history of breast cancer -- Women who have had breast cancer face an increased risk of getting breast cancer in the other breast.
Family history -- Risk for developing breast cancer increases if a close relative (mother, sister, or daughter) has had breast cancer, especially at a young age. In families where many women have had the disease, gene testing can sometimes show the presence of specific genetic changes that increase the risk of breast cancer. Doctors may suggest ways to try to delay or prevent breast cancer, or to improve the detection of this disease in women who have these changes in their genes.
Certain breast changes -- Having a diagnosis of atypical hyperplasia or lobular carcinoma in situ (LCIS) may increase the risk of breast cancer.
Other factors associated with an increased risk for breast cancer include:
Estrogen -- Evidence suggests that the longer a woman is exposed to estrogen (made by the body, taken as a drug, or delivered by a patch), the higher the risk of developing breast cancer. The risk is somewhat increased among women who began menstruation at an early age (before age 12), experienced late menopause (after age 55), never had children, or took Hormone Replacement Therapy (HRT) for extended periods of time.
Late childbearing -- Women who have their first child late (after about age 30) have a greater chance of developing breast cancer than women who have a child at a younger age.
Breast density -- Breast cancers nearly always develop in lobular or ductal (dense) tissue rather than in fatty tissue. Breast cancer is more likely to occur in breasts that have a lot of dense tissue. It is also more difficult to see abnormal areas on a mammogram when breasts are dense.
Radiation therapy -- Women whose breasts were exposed to radiation during radiation therapy before age 30 are at an increased risk for developing breast cancer. Studies show that the younger a woman was when she received treatment, the higher the risk for developing breast cancer later in life.
Alcohol -- Some studies suggest a slightly higher risk of breast cancer among women who drink alcohol.
It is important to know that most of the women who develop breast cancer have none of the risk factors listed above, other than the risk that comes with growing older.