Atypical hyperplasia is a benign (noncancerous) cellular hyperplasia in which cells show some atypia. In this condition, cells look abnormal under a microscope and are increased in number.

Atypical hyperplasia is a high-risk premalignant lesion of the breast. It is believed that atypical ductal hyperplasia (ADH) is a direct precursor for low-grade mammary ductal carcinoma, whereas atypical lobular hyperplasia (ALH) serves as a risk indicator.

• Atypical hyperplasia entry in the public domain NCI Dictionary of Cancer Terms

 This article incorporates public domain material from Dictionary of Cancer Terms. U.S. National Cancer Institute.

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