Atypical Hyperplasia


What is atypical hyperplasia?

Atypical hyperplasia (or atypia) means that there are abnormal cells in breast tissue taken during a biopsy. (A biopsy means that tissue was removed from the body for examination in a laboratory.) These abnormal cell collections are benign (not cancer), but are high-risk for cancer.

Findings of atypical hyperplasia account for 10% of benign breast biopsies. There are two types of atypical hyperplasia — atypical ductal hyperplasia (ADH) and atypical lobular hyperplasia (ALH).

Atypical ductal hyperplasia means that abnormal cells are located in a breast duct. Atypical lobular hyperplasia means that abnormal cells are in a breast lobule (the milk-making parts of the breast). Another high-risk lesion is lobular carcinoma in situ (LCIS), which is more extensive involvement of atypical cells in the breast lobules.

What does having atypical hyperplasia mean?

If your breast biopsy shows atypical hyperplasia, this doesn’t mean that you have cancer. The cells are a marker for increased breast cancer risk. Studies have shown that women with atypical hyperplasia have up to a four times increase in breast cancer risk. This is especially true for estrogen receptor-positive breast cancer.

Long-term data have shown that the younger a woman is at the time of her diagnosis of atypical hyperplasia, the more likely she is to develop breast cancer later in life. Specifically, five years after the diagnosis of atypical hyperplasia, 7% of women will develop breast cancer. Ten years after the diagnosis, 13% of these women will develop cancer. Twenty-five years after the diagnosis, 30% of these women will develop breast cancer.

What is estrogen receptor-positive breast cancer?

Most breast cancer cells respond to hormones, specifically estrogen or progesterone. These hormones circulate in the blood. A cancer is called estrogen receptor-positive if it responds to estrogen. This means that estrogen triggers the cancer to grow. Progesterone receptor-positive breast cancer means that progesterone triggers the cancer to grow.

Knowing which hormone makes the cancer grow helps to determine the best way to treat or prevent breast cancer. One study showed that of the women who did develop breast cancer, 88% of the breast cancers were estrogen receptor-positive.

Management and Treatment

What kind of follow-up care is needed after a diagnosis of atypical hyperplasia?

Surgery is usually performed to remove the entire area of tissue where the atypical cells were found. In up to 20% of cases, cancer may be found after a final exam of the removed breast tissue. After surgery, increased screening is recommended. Clinical breast exams will be done every six months and you’ll have annual mammograms. As an adjunct, some patients may also have high risk screening annual MRIs, alternating with the mammogram; which means you will undergo breast imaging every six months. Your medical breast specialist will help determine if you qualify for an annual breast MRI based on your risk factors. An MRI is especially helpful if you are a woman with dense breast tissue.

Care at Cleveland Clinic


What can I do to decrease my risk of breast cancer?

Women with atypical hyperplasia may benefit greatly from taking a five-year course of certain medications. These medications block estrogen and help decrease the risk of estrogen receptor-positive invasive breast cancer. The effects can remain for up to 15 years after taking them.

Tamoxifen (Nolvadex®) is recommended for women who aren’t yet in menopause. Other drugs are recommended for women in menopause. Menopause is defined as the absence of your menstrual period for 12 months. The medications for menopausal women are:

  • Raloxifene (Evista®).
  • Exemestane (Aromasin®).
  • Anastrozole (Arimidex®).

All of these medications have some side effects. However, the number of serious side effects is very low.

You’ll have to have a detailed discussion with your healthcare provider to determine if these medications or other treatments are right for you. In some extreme cases, risk-reducing mastectomies (removal of the breasts) are considered. However, this isn’t a routine recommendation.

It’s helpful to become familiar with your own breast tissue to help identify changes that should be reported to your provider. Therefore do your best to perform self-breast checks, also called self-breast awareness.

Obesity is a known risk factor for breast cancer. Maintaining a healthy weight and active lifestyle will help to decrease one’s risk. Drinking alcohol is an under-recognized risk factor for breast cancer. Regularly drinking beverages that contain alcohol (three to six drinks a week) can increase the risk of breast cancer an additional 15%. Therefore, avoid or minimize alcohol intake to less than one glass per day. Smoking is a known risk factor, not just for breast cancer, but other cancers and illnesses (heart and lung disease; increases the aging process). Do your best to avoid smoking, including second hand smoke.

Last reviewed by a Cleveland Clinic medical professional on 12/15/2020.


  • Hartman LC, Degnim AC, Santen RJ, Dupont WD, Ghosh K. Atypical hyperplasia of the breast – risk assessment and management options. N Engl J Med. 2015;372(1):78-89.
  • American Cancer Society: Hyperplasia of the Breast (Ductal or Lobular). ( Accessed 12/29/2020.
  • Chen W, Rosner B, Hankinson SE, et al. Moderate alcohol consumption during adult life, drinking patterns, and breast cancer risk. JAMA 2011; 306:1884–1890.
  • Hartmann LC. Radisky DC, Frost MH, et al. Understanding the Premalignant Potential of Atypical Hyperplasia through Its Natural History: A Longitudinal Cohort Study. Cancer Prev Res February 2014 7; 211.
  • Susan G Komen. Hyperplasia and Other Benign Breast Conditions. ( Accessed 12/29/2020.

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