What Happens

Breast cancer occurs when cells in the breast grow abnormally. As the breast cancer grows, it can spread to nearby tissues and lymph nodes. Advanced breast cancer can affect the bones, liver, and brain.

Your doctor will find out more about your breast cancer when the cancer cells are examined under the microscope. Tests for hormone receptors and gene changes are usually done after surgery. For the tests, your doctor uses tissue taken from your breast.

Your doctor will also stage the cancer to see how far it has spread within the breast, to nearby tissues, and to other organs. Your doctor will find the stage by using tests, such as chest X-rays or CT scans. The stage of your cancer will help guide your treatment options.

What Increases Your Risk

Although the exact cause of breast cancer is not known, most experts agree that several things can increase your risk of breast cancer.

Top risk factors linked to breast cancer

• Aging. Your breast cancer risk increases as you get older. By age group, breast cancer is diagnosed in:³
  • 4 out of 1,000 women in their 30s.
  • 15 out of 1,000 women in their 40s.
  • 24 out of 1,000 women in their 50s.
  • 35 out of 1,000 women in their 60s.
• Being female. Although breast cancer can occur in men, most breast cancer is found in women.

Conditions that can raise your risk of breast cancer

• Personal history. Women who have dense breasts, a breast disease that is not cancer, or who have had breast cancer before have an increased risk.
• Family history. A woman's risk of breast cancer increases if her mother, sister, daughter, or two or more other close relatives, such as cousins, have a history of breast cancer, especially if they were diagnosed with breast cancer at age 50 or younger.
  • A small number of women who have a family history of breast cancer have inherited changes to certain genes, such as BRCA1 or BRCA2, that increase their breast cancer risk.
  • Genetic tests are available to find out if you have the genetic mutations long before any cancer appears.

    Breast Cancer Risk: Should I Have a BRCA Gene Test?

• Breast changes. Some breast changes, such as having atypical hyperplasia, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS), increase a woman's risk for breast cancer.

Other things that increase the risk of breast cancer

• Race. Breast cancer occurs more often in white women than in black, Hispanic, or Asian women.
• Radiation therapy. Women whose breasts were exposed to significant amounts of radiation at a young age, especially those who were treated for Hodgkin's lymphoma, have an increased risk for breast cancer.
• Not breast-feeding. Women who don't breast-feed have a higher risk of breast cancer than those who breast-feed. The more months of breast-feeding, the lower the breast cancer risk.
• Alcohol. Your risk goes up the more you drink. For the best health, women should have no more than 1 drink a day or 7 drinks a week.
• Hormones. Female hormones play a part in some types of breast cancer. Your risk of breast cancer is higher if:⁴
  • You use estrogen-progestin hormone therapy after menopause for several years or more.
  • You begin menstruation before age 12 and start menopause later than age 55.
  • You have your first baby at a later age or you do not bear any children.
  • You have extra body fat or gain weight later in life. These can increase the amount of estrogen in your body.

For more information about your personal risk level, go to www.cancer.gov/bcrisktool.