Fat Necrosis and Oil Cysts in the Breast

Fat necrosis is a benign (non-cancerous) breast condition that happens when an area of the fatty breast tissue is damaged, usually as a result of injury to the breast. It can also happen after breast surgery or radiation treatment. Fat necrosis is more common in women with very large breasts.

As the body repairs the damaged breast tissue, it’s usually replaced by firm scar tissue. But some fat cells may respond differently to injury. Instead of forming scar tissue, the fat cells die and release their contents. This forms a sac-like collection of greasy fluid called an oil cyst.


Oil cysts and areas of fat necrosis can form a lump that can be felt, but it usually doesn’t hurt. The skin around the lump might look thicker, red, or bruised. Sometimes these changes can be hard to tell apart from cancers on a breast exam or even a mammogram. If this is the case, a biopsy (removing all or part of the lump to look at the tissue under the microscope) might be needed to find out if the lump contains cancer cells.

Doctors can usually tell an oil cyst by the way it looks on an ultrasound. But if there’s a concern that it might be something else, a needle aspiration biopsy might be done, in which a thin, hollow needle is put into the cyst to take out the fluid for testing.


Fat necrosis and oil cysts usually don’t need to be treated. Sometimes fat necrosis goes away on its own. If a needle aspiration is done to remove the fluid in an oil cyst, it can also serve as treatment.

If the lump or lumpy area gets bigger or becomes bothersome, however, surgery may be done.

How do fat necrosis and oil cysts affect your risk for breast cancer?

These breast changes do not increase a woman’s risk of breast cancer.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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Last Medical Review: September 10, 2019 Last Revised: September 10, 2019

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