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Fat necrosis is a benign (non-cancerous) breast condition that can develop when an area of fatty breast tissue is injured. It can also develop after breast surgery or radiation treatment.
There are different stages of fat necrosis. As the fat cells die, they release their contents, forming a sac-like collection of greasy fluid called an oil cyst. Over time, calcifications (small deposits of calcium) can form around the walls of the cyst, which can often be seen on mammograms. As the body continues to repair the damaged breast tissue, it's usually replaced by denser scar tissue.
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 breast 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 a mammogram or breast ultrasound. But if it could be something else, some type of needle biopsy (a fine needle aspiration or core needle biopsy) might be done.
These breast changes do not affect your risk for breast cancer.
As long as doctors are sure of the diagnosis, fat necrosis and oil cysts usually don’t need to be treated. Sometimes fat necrosis goes away on its own. If a needle biopsy is done to remove the fluid in an oil cyst, it can also serve as treatment.
If the lump gets bigger or becomes bothersome, however, surgery may be done to remove it.
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 Revised: January 25, 2022
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