A fluid-filled sac in the breast that most often isn't cancer.

Breast cysts are common before menopause, most often before age 50. Many go away with no treatment. After menopause, breast cysts are common in people who use hormone therapy.

Breast cysts can be in one or both breasts. A cyst may feel like a grape or water balloon or feel firm. There can be more than one cyst.

Treatment most often isn't needed. But if a cyst is large or causes discomfort, it can be drained with a needle.