Merck Manual

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Breast Cysts

By

Lydia Choi

, MD, Karmanos Cancer Center

Reviewed/Revised Jun 2022 | Modified Sep 2022
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Breast cysts are fluid-filled sacs that develop in the breast.

Breast cysts are common. In some women, cysts develop frequently, sometimes with other changes in fibroglandular tissue (composed of fibrous connective tissue and glands) in the breast. Cysts when accompanied by these changes (including pain and general lumpiness) are called fibrocystic changes Fibrocystic Changes of the Breast Fibrocystic changes of the breast (formerly called fibrocystic breast disease) include breast pain, cysts, and lumpiness that are not due to cancer. (See also Overview of Breast Disorders and... read more .

The cause of breast cysts is unknown, although injury may be involved.

The Breasts
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Breast cysts can be tiny or several inches in diameter.

Cysts sometimes cause breast pain Breast Pain Many women experience breast pain. Breast pain may occur in one or both breasts. (See also Overview of Breast Disorders.) Likely causes of breast pain depend on whether the pain is felt in a... read more . To relieve the pain, a doctor may drain fluid from the cyst with a thin needle (called aspiration). The fluid is examined under a microscope to check for cancer only if any of the following occurs:

  • The fluid is bloody or cloudy.

  • Little fluid is obtained.

  • The lump is still present after the fluid is drained.

Otherwise, the woman is checked again in 4 to 8 weeks. If the cyst can no longer be felt at this time, it is considered noncancerous. If it has reappeared, it is drained again, and the fluid is examined under a microscope. If the cyst reappears a third time or if it is still present after it was drained, a biopsy is done.

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