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 therapy. As the body repairs the damaged tissue, it is replaced by firm scar tissue.

Because most breast cancers are also firm, areas of fat necrosis with scarring can be hard to tell from cancers by a breast exam. It may also be hard to tell the difference on a mammogram. A needle biopsy, or sometimes an excisional biopsy, may be needed to learn if cancer is present.

Fat necrosis is more common in women with very large breasts. It does not increase a woman's risk of developing breast cancer.

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 can be diagnosed by fine needle aspiration. This can also serve as treatment, but it is not usually needed unless the cyst is bothersome.