What are breast cysts?

Cysts are fluid-filled sacs that grow inside the breasts. These sacs form when normal milk glands in the breast get bigger. A woman can have a single cyst or many cysts at a time. Breast cysts range in size from smaller than a pea to larger than a ping pong ball.

Breast cysts are common, particularly in women age 40-60. Although larger cysts can sometimes be felt as “lumps,” many cysts cannot be felt by physical examination. Cysts that cannot be felt may be found during a mammogram or ultrasound.

When a mammogram shows a possible cyst, a breast ultrasound is usually done. An ultrasound shows whether the lump is a fluid-filled cyst or a solid lump. It also shows whether a cyst is a “simple cyst” or “complex cyst.” Breast ultrasound is the best way to identify and diagnose breast cysts because it is accurate 95 to 100% of the time. 

Do cysts lead to cancer?

Almost all breast cysts identified as “simple cysts” by ultrasound are benign and never become cancerous. It is estimated that one in 1,000 cysts contain a tumor (but they are usually benign). These tumors can be identified by ultrasound in most cases. Women with cysts are not at greater risk for cancer although this risk may be slightly higher if there is a family history of breast cancer (mother, sister, or daughter).

Do cysts need to be aspirated (drained)?

When a breast lump is found your doctor may use a simple and effective technique called needle aspiration to find out what is in the lump. If the lump is a fluid-filled cyst, the needle can remove the fluid which usually makes the lump disappear. If no fluid is found, the lump is not a cyst and whatever material is aspirated is sent to the laboratory for analysis.

When a cyst is discovered by ultrasound, aspiration is not generally recommended unless the cyst looks unusual on the ultrasound image. Aspiration may also be done if the patient wants to relieve physical or emotional discomfort caused by the cyst. If the ultrasound shows that the cyst may contain material other than fluid, the doctor may recommend aspirating the cyst. This is done using ultrasound guidance to make sure the cyst is completely drained.

Does cyst fluid need to be analyzed in the laboratory?

Normal benign cyst fluid is usually yellow, green or gray and does not need to be analyzed in a laboratory. Studies of breast cyst fluid from thousands of women show that analysis of fluid is important only when the color of the fluid suggests previous bleeding.

What will happen if a cyst is left alone?

Breast cysts often change in size. Breast cysts can look different or disappear entirely on mammograms from one year to the next. This is why we recommend diagnostic rather than screening mammograms for our patients with “cystic breasts” and changing lumps. Diagnostic mammograms allow the doctor to complete an ultrasound at the same appointment as the mammogram to make sure the changes are actually due to cysts and not solid lumps.