Atypical hyperplasia of the breast

Hyperplasia is an abnormal increase in the number of cells in a tissue. In hyperplasia of the breast, there is an overgrowth of cells that line the ducts and lobules of the breast. Women with hyperplasia of the breast have a slightly greater risk of developing breast cancer.


In hyperplasia, the cells are fast growing but they usually look much like normal breast cells. With atypical hyperplasia, the fast-growing cells do not look like normal breast cells.

  • Atypical ductal hyperplasia is an overgrowth of the cells lining the ducts. This is the most common form of atypical hyperplasia of the breast.
  • Atypical lobular hyperplasia is an overgrowth of the cells lining the lobules.


Women with atypical hyperplasia have a higher risk of developing breast cancer than women without the condition. The risk of breast cancer is even higher in women:

  • with a family history of breast cancer
  • who are diagnosed with atypical hyperplasia before menopause


Breast cancer is more likely to develop in the breast where the atypical hyperplasia is found, although cancer can develop in the opposite breast. The risk of developing breast cancer is greatest 10–15 years after diagnosis of atypical hyperplasia. The risk begins to decline after this period.

Risk factors

It is not known what causes hyperplasia or atypical hyperplasia and there are no known risk factors.


Women who are at higher than average risk for developing breast cancer because of atypical hyperplasia should talk to their doctor about a personal plan of testing.


Women with atypical hyperplasia may need to be tested at a younger age and more often than women at average risk for breast cancer. A personal plan of testing may include:

Signs and symptoms

Atypical hyperplasia does not cause any signs or symptoms. It is often found during a mammography.


Atypical hyperplasia is diagnosed with either:


Treatment options for atypical hyperplasia of the breast may include:


Selective estrogen-receptor modulators (SERMs) are anti-estrogen drugs that block the effects of estrogen in some tissues (such as breast tissue) and act like estrogen in other tissues. Some SERMs like tamoxifen (Nolvadex, Tamofen) are used to treat breast cancer. Tamoxifen lowers the risk of developing breast cancer in women at high risk of developing the disease, but it also increases the risk of uterine (endometrial) cancer.


Chemoprevention may be offered to women with atypical hyperplasia, especially if they have other risk factors for breast cancer, such as a family history of the disease. Women with atypical hyperplasia should talk to their doctor about the benefits and possible risks of taking tamoxifen or other SERMs to reduce the risk of breast cancer




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