​Atypical hyperplasia is an accumulation of abnormal cells in the breast and it is a risk factor for developing breast cancer.

Atypical ductal hyperplasia is caused by the accumulation of abnormal cells that are similar to the breast duct cells.

Atypical lobular hyperplasia is caused by abnormal cells similar to the breast lobule cells.

There are no known causes.

​Atypical hyperplasia is usually asymptomatic and may present as an abnormal finding, such as microcalcifications on mammograms, but it is most often discovered incidentally when biopsies are done for other findings.

​A biopsy of the abnormal area seen on mammogram may be recommended. This may be done using a needle biopsy or by open biopsy. An open biopsy allows more tissue to be examined and in about 25 percent of cases, an early cancer may be found.

​The main form of treatment is surgery and the removal of the abnormal area.

Atypical hyperplasia ​Cancer Risk

There is an increased risk of developing breast cancer in the future. It is about four times the lifetime risk.

At 5 years after the diagnosis of atypical hyperplasia, 7 percent of the women may develop breast cancer. At 10 years after the diagnosis, 13 percent may develop breast cancer and at 25 years after the diagnosis, about 30 percent may develop breast cancer.

The risk of cancer may be decreased by taking oral medications like Tamoxifen, Raloxifene, aromatase inhibitors and avoiding hormonal replacement therapy.

Follow-up Care

Women with atypical hyperplasia should continue with monthly breast self-examinations in order to detect any early breast changes as well as consider annual mammograms, in view of the increased risk.