The term “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. Less commonly, breast cancer can begin in the stromal tissues, which include the fatty and fibrous connective tissues of the breast. Over time, cancer cells can invade nearby healthy breast tissue and make their way into the underarm lymph nodes, small organs that filter out foreign substances in the body. If cancer cells get into the lymph nodes, they then have a pathway into other parts of the body.

About 1 in 8 women in the United States — 12%, or about 12 out of every 100 — can expect to develop breast cancer over the course of an entire lifetime. In the U.S., an average lifetime is about 80 years. So, it’s more accurate to say that 1 in 8 women in the U.S. who reach the age of 80 can expect to develop breast cancer. In each decade of life, the risk of getting breast cancer is actually lower than 12% for most women.

Initially, breast cancer may not cause any symptoms. A lump may be too small for you to feel or to cause any unusual changes you can notice on your own. Often, an abnormal area turns up on a screening mammogram (X-ray of the breast), which leads to further testing.

According to the American Cancer Society, any of the following unusual changes in the breast can be a symptom of breast cancer:

• swelling of all or part of the breast
• skin irritation or dimpling
• breast pain
• nipple pain or the nipple turning inward
• redness, scaliness, or thickening of the nipple or breast skin
• a nipple discharge other than breast milk
• a lump in the underarm area

These changes also can be signs of less serious conditions that are not cancerous, such as an infection or a cyst. It’s important to have any breast changes checked out promptly by a doctor. This is why regular mammograms are important!

Women between 40 and 44 have the option to start screening with a mammogram every year. Woman 45-54 should get mammograms every year. Women 55 and older can choose to switch to a mammogram every other year or continue yearly mammograms.

Finding breast cancer early and getting treatment are the most important strategies to prevent deaths from breast cancer. Breast cancer that is found early, when it is small and has not spread, is easier to treat successfully.