Atypical hyperplasia of the breast

This page was reviewed under our medical and editorial policy by

Daniel Liu, MD, Plastic and Reconstructive Surgeon, CTCA Chicago.

This page was updated on May 4, 2022.

Atypical hyperplasia itself isn't cancer, but it may increase your risk of breast cancer in the future. About 10 percent of all benign breast biopsies turn out to be atypical hyperplasia, according to a June 2018 review in the Journal of Clinical Oncology.

What is atypical hyperplasia?

Atypical hyperplasia is what happens when the cells that line the ducts or lobules of the breast grow out of control. Normally, both ducts and lobules are lined with two layers of cells. When these cells grow rapidly, they’re no longer lined up like they're supposed to be.

Under a microscope, the cells that are growing out of control can be classified in two ways.

Usual hyperplasia means that while the cells are more numerous than they should be, they still look normal in appearance. On the other hand, cells that look unusual or distorted are called atypical hyperplasia.

Atypical hyperplasia can be broken down further into two categories:

  • Atypical ductal hyperplasia (ADH)
  • Atypical lobular hyperplasia (ALH)

Both ADH and ALH have the same explosion of cell growth, as well as the same risk of cancer development, but the causes are still unknown.

Interestingly, this classification doesn't really have to do with the actual location of the abnormal cells—hyperplasia isn't named ductal or lobular if it occurs in either the ducts or the lobules. It has more to do with how the cells look under a microscope.

Atypical ductal hyperplasia (ADH)

Atypical ductal hyperplasia occurs when cells that typically line the milk ducts grow unchecked and out of control. Ducts are the small tubes within the breast that carry milk to the nipples. In ADH, some features are the same as ductal carcinoma in situ (DCIS). DCIS is considered stage 0 breast cancer, where the abnormal cells haven't spread beyond the ducts. While DCIS is considered early-stage breast cancer, hyperplasia itself just increases the risk of developing cancer.

Atypical lobular hyperplasia (ALH)

Atypical lobular hyperplasia has the same prolific cell growth as ADH, but refers to the cells that line the cluster of glands that produce milk (also called lobules).

Connection to breast cancer

Atypical hyperplasia increases your chance of getting breast cancer, but usual hyperplasia may or may not affect your cancer risk. Some usual hyperplasias don’t increase the risk of breast cancer, while others can make it one and a half to two times more likely that you’ll have breast cancer, according to the American Cancer Society.

With atypical hyperplasia, where cells appear distorted under the microscope, it means your chances of breast cancer are four to five times higher.

Symptoms and diagnosis

Atypical hyperplasia doesn't usually have a lump in the breast or any breast changes you can typically feel. However, your doctor may be able to see it on a mammogram.

To be able to diagnose it properly, you’ll likely need a breast biopsy. This means your doctor may study a small sample of breast tissue taken through a hollow needle. Or, instead of taking a sample, your care team may opt for surgery to remove the affected breast tissue.


Most of the time, usual hyperplasia doesn’t require treatment. If you’re diagnosed with atypical hyperplasia, both ADH and ALH, your doctor may recommend surgically removing it—and possibly the tissue around it, especially if it’s ADH.

If ALH is discovered after a biopsy, there’s some debate about the best way forward. You may undergo an additional surgery to make sure all the abnormal cells are removed and there isn't anything else concerning in the area, or you may simply be monitored with regular physical exams and mammograms.

Follow up

If you have atypical hyperplasia, in addition to a yearly mammogram, you may need to see your doctor more often for monitoring. You may also need to have a breast MRI performed. 

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