Breast Cysts

Breast cysts are fluid-filled sacs that grow to be as small as a few millimeters (the size of a crayon’s tip) to as large as two inches (the size of a lime). Some cysts are so tiny they are only spotted during routine mammograms, while other, larger cysts can result in pain and discomfort. Most breast cysts are not cancerous (benign) and do not increase your risk of breast cancer.

Breast cysts can occur at any age, but are most common for women in their 30s and 40s.

Most often, breast cysts show up as lumps in the breast. If a cyst is large enough to be felt, it’s usually round and fairly movable under the skin. Breast cysts can be painful or tender and may cause nipple discharge. These symptoms may change at different points in the menstrual cycle. 

If you’re concerned about changes in your breasts, you may want to talk with your doctor.

To diagnose a breast cyst, your doctor will likely ask you questions about any personal or family history of breast cancer and may use an ultrasound to get a closer look at the cyst. 

There are three categories of breast cysts:

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  Simple cysts have smooth, thin, regularly shaped walls and are completely filled with fluid. Simple cysts are always benign. They may occur as part of broader fibrocystic breast changes, which are not dangerous. 

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  Complex cysts have irregular or scalloped borders, thick walls, and contain fluid as well as some solid areas

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  Complicated cysts have thin walls like simple cysts, but they contain some solid areas inside them. 

Keep in mind that many radiologists (physicians who perform and read imaging studies) use the terms “complicated” and “complex” interchangeably. If your health team uses either term when describing your cyst, ask for clarification about the specific nature of your cyst. 

Most simple cysts will improve on their own. If you have a simple cyst that is especially large, uncomfortable, or painful, your doctor may drain it. Most of the time, the cyst will not return and women will return to routine breast cancer screening. If it comes back, it may be evaluated again with a mammogram and ultrasound and drained again. 

If you have a complicated or complex cyst, your doctor might recommend that you have the fluid drained so that it can be tested. They may also ask to see you every six to 12 months for one to two years to check on the cyst. 

If a cyst has features that suggest it could be cancerous, your doctor can do a procedure called a biopsy to get a better look. Often, doctors will use ultrasound to guide a needle into the cyst and remove a piece of it. They can then examine the sample under a microscope. Your doctor may remove the whole cyst (excisional biopsy), but that is rare.

If you have multiple cysts or you develop new cysts frequently, you may want to see a breast specialist. Your doctor can refer you to a qualified specialist near you.

Scientists do not know the exact cause of breast cysts. They do know that the development of breast cysts is related to hormonal changes, most commonly around a menstrual period. Breast cysts are more common in women who are between 30 and 50 years old and still have a menstrual period (pre-menopausal). While less common after menopause, women taking hormone therapy may have a higher risk of developing breast cysts. 

Simple cysts that go away once they’re drained are not cancerous. Complex cysts can be cancerous (malignant) but more often they are not cancerous (benign). 

While a mammogram may spot a breast cyst, a breast ultrasound is better at determining whether the cyst is filled with fluid, solid areas, or a combination of both. 

There is only a small chance that a breast cyst will rupture on its own. Rupture may lead to infection, inflammation, or an immune response.