Atypical hyperplasia of the breast refers to accumulation of abnormal cells in the breast and is considered to be a precancerous condition that affects cells in the breast. It is not cancer, but can be a forerunner to the development of breast cancer. In cases when the atypical hyperplasia cells keep dividing and becoming abnormal, the condition can develop into noninvasive breast cancer (carcinoma in situ) or invasive breast cancer. Intensive breast cancer screening and medications to reduce breast cancer risk are recommended when a condition of atypical hyperplasia of the breast occurs.


Atypical hyperplasia usually does not cause any specific symptoms.


It is not clear what causes atypical hyperplasia. Atypical hyperplasia forms when breast cells become abnormal in number, size, shape, growth pattern and appearance. The appearance of the abnormal cells determines the type of atypical hyperplasia:

  • Atypical ductal hyperplasia which causes abnormal cells to appear similar to the cells of the breast ducts.
  • Atypical lobular hyperplasia which causes abnormal cells to appear similar to the cells of the breast lobules.

Risk Factors

Researchers have discovered that women with atypical hyperplasia of the breast are at higher risk for developing breast cancer.


Women diagnosed with atypical hyperplasia have an increased risk of developing breast cancer in the future. It is about four times higher than that of women who do not have atypical hyperplasia. The risk of breast cancer is the same for women with atypical ductal hyperplasia and women with atypical lobular hyperplasia.

Being diagnosed with atypical hyperplasia at a younger age may increase the risk of breast cancer even more. For example, women diagnosed with atypical hyperplasia before age 45 seem to have a greater risk of developing breast cancer during their lifetimes.


In most cases, atrioventricular canal defect cannot be prevented. Consulting a genetic counselor and a cardiologist before getting pregnant is recommended.