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Atypical hyperplasia in a breast lump

Atypical hyperplasia is a non cancerous (benign) condition. It’s when the cells in the breast increase in number and also develop an unusual shape.

Breasts are made up of:

  • fat
  • glandular tissue divided into lobes (each containing lots of lobules)
  • a network of ducts or milk ducts
  • connective tissue

The ducts spread from the lobes towards the nipple.

Diagram showing the lobes and ducts of a breast

Atypical hyperplasia can occur in the ducts (atypical ductal hyperplasia or ADH) or the lobules (atypical lobular hyperplasia or ALH).

Atypical cells mean that the cells are not entirely normal. Normal cells go through quite a few changes before they become cancerous.

The cells may not necessarily become cancer cells. The cells might not change further. Or they may die off or go back to normal.

Does atypical hyperplasia affect the risk of breast cancer?

Atypical hyperplasia can increase your risk of developing breast cancer in the future.

Who gets it atypical hyperplasia?

Atypical hyperplasia can sometimes develop as the breast changes with age. It can affect women of any age, but is more common in women over 35.

Diagnosing atypical hyperplasia

Atypical hyperplasia is usually found by chance after a routine mammogram or when tissue from a biopsy or breast surgery is examined under a microscope in the laboratory. 

Treatment for atypical hyperplasia

Your specialist may recommend a small operation to ensure all of the hyperplasia has been removed. This will then be examined in the laboratory under a microscope. 

There is no danger that any of the cells will have spread, if the cells removed are not cancer cells. But if the lump is left and it does become cancerous in the future, then there is a risk that some of the cells could break away from the lump and spread elsewhere in the body.

Follow up

Your specialist might want you to have follow up appointments. These may include clinic visits and a mammogram every one to two years. How often, and for how long, you go for follow-up appointments will depend on your situation. 

Go to your doctor if you notice any new breast changes. You don't need to wait for your clinic visit.

Breast cancer protective factors

Some factors can help to reduce the risk of breast cancer in general. These include:

  • being physically active
  • having a healthy diet and limiting the amount of alcohol you have
Last reviewed: 
10 Mar 2020
Next review due: 
10 Mar 2023
  • Overview of benign breast disease

    UpToDate, last updated September 2020

  • Atypical Hyperplasia of the Breast – Risk Assessment and Management Options

    LC Hartmann and others

    New England Journal of Medicine, 2015. Volume 372

  • Assessment of breast mass

    BMJ Best Practice, Last updated September 2018

  • Reassessing risk models for atypical hyperplasia: age may not matter

    E Mazzola and others

    Breast Cancer Research and Treatment, 2017. Volume 165, Issue 2