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BreastCancer.org says breast cancer refers to a malignant tumor that has developed from cells in the breast. Usually breast cancer either begins in the cells of the lobules, which are the milk-producing glands, or the ducts, the passages that drain milk from the lobules to the nipple.
According to the American Cancer Society, breast cancer is the most common cancer among American women, except for skin cancers. The chance of developing invasive breast cancer at some time in a woman's life is a little less than 12 percent. The disease occurs mostly in women, but men can also get it.
National Center for Biotechnology Information (NCBI) says there are two main types of breast cancer. Most breast cancers are ductal carcinoma which starts in the ducts. The other is lobular carcinoma which starts in the lobules.
There are several risk factors for breast cancer that women have no control over. These include age and gender; family history of breast cancer; genetic makeup; and menstrual cycles. NCBI reports women who started their periods before age 12 or went through menopause after age 55 have an increased risk for breast cancer.
The American Cancer Society says the risk factors women can control include being overweight, alcohol consumption and smoking.
NCBI says women have a higher risk for breast cancer if they have received hormone replacement therapy with estrogen for several years or more. Plus women who have never had children or who had them only after age 30 have an increased risk for breast cancer The American Cancer Society adds using oral contraceptives appears to slightly increase a woman’s risk for breast cancer, but only for a limited period of time.
BreastCancer.org says initially breast cancer may not cause any symptoms. Often, an abnormal area turns up on a screening mammogram, which leads to further testing. This is why regular breast exams are so important.
NCBI reports symptoms may include a breast lump or lump in the armpit that is hard, has uneven edges, and usually does not hurt. BreastCancer.org adds that cancers can be tender, soft, and rounded.