Adenosis of the Breast

In adenosis the breast lobules (milk-producing glands) are enlarged, and there are more glands than usual. Adenosis is often found in biopsies of women who have fibrocystic changes.

There are many names for this benign breast condition, including aggregate adenosis, tumoral adenosis, or adenosis tumor. Even though some of these terms contain the term tumor, adenosis is not breast cancer.

Sclerosing adenosis is a special type of adenosis in which the enlarged lobules are distorted by scar-like fibrous tissue. This type may cause breast pain.


If many enlarged lobules are close to one another, they may be large enough to be felt as a breast lump. In cases like this, a breast exam may not be enough to tell if the lump is adenosis or a breast cancer.

Calcifications (mineral deposits) can form in adenosis, in sclerosing adenosis, and in breast cancers. These can show up on mammograms, which can make it hard to tell these conditions apart.

Because of these uncertainties, a biopsy is usually needed to know if the breast change is caused by adenosis or cancer. (In a biopsy, a small piece of tissue is removed and checked under a microscope.)


Women with adenosis do not need treatment, but might be watched closely. 

How does adenosis affect your risk for breast cancer?

Adenosis is not thought to increase breast cancer risk, although some studies have found that women with sclerosing adenosis have a slightly higher risk of developing breast cancer.1

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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National Cancer Institute. Understanding Breast Changes: A Health Guide for Women. April 23, 2015. Accessed at on June 10, 2016.

Santen RJ, Mansel R. Benign breast disorders. N Engl J Med. 2005;353:275-285.

Schnitt SJ, Collins LC. Pathology of benign breast disorders. In: Harris JR, Lippman ME, Morrow M, Osborne CK, eds. Diseases of the Breast. 4th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2010:69-85.

1 Visscher DW, Nassar A, Degnim AC, et al. Sclerosing adenosis and risk of breast cancer. Breast Cancer Res Treat. 2014;144:205-212.

Last Medical Review: March 16, 2015 Last Revised: April 21, 2016

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