Non-Cancerous Breast Conditions

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Fat necrosis and oil cysts

Fat necrosis 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 surgery or radiation treatment. As the body repairs the damaged tissue, it’s replaced by firm scar tissue.

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. These can be hard to tell apart from cancers by a breast exam or even a mammogram. A biopsy (removing all or part of the lump to look at the tissue under the microscope) may be needed to learn if cancer is present.

Oil cysts (like other cysts) can be seen on ultrasound and then diagnosed by needle aspiration, where a thin needle is put into the cyst to take out the fluid. This can also serve as treatment, but it’s not usually needed unless the cyst is bothersome.

Link to cancer risk

Fat necrosis is more common in women with very large breasts. It doesn’t increase a woman’s risk of developing breast cancer.

Last Medical Review: 03/16/2015
Last Revised: 06/10/2015