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Breast cysts are fluid-filled sacs that develop in the breast.

Breast cysts are common. In some women, many cysts develop frequently, sometimes with other fibrocystic changes. The cause of breast cysts is unknown, although injury may be involved. Breast cysts can be tiny or several inches in diameter.

Cysts sometimes cause breast pain. To relieve the pain, a doctor may drain fluid from the cyst with a thin needle. Sometimes the fluid is examined under a microscope to check for cancer. The color and amount are noted. If the fluid is bloody, brown, or cloudy or if the cyst does not disappear or reappears within 12 weeks after it is drained, the entire cyst is removed surgically because cancer in the cyst wall, although rare, is possible.

Last full review/revision November 2008 by Victor G. Vogel, MD, MHS