In some women, female hormones can cause cysts, which are sacs of fluid, to develop in breast tissue. Cysts are almost always benign. They are often painful, but they may not cause any symptoms at all. They can get larger or smaller, and sometimes go away on their own. They can be single or multiple, in one or both breasts. Cysts can occur at any age, but are most commonly seen in women between the ages of forty and fifty, in the 5-10 years prior to menopause. This tends to be a time of hormonal fluctuations and women often experience irregular menstrual periods at this time as well. Because they have a hormonal basis, cysts tend to regress after menopause, and are less common in this age group unless a woman takes hormone replacements or is overweight, because precursors are converted to estrogen in fatty tissue.
Cysts can cause breast lumps on breast exam or masses on mammogram. An ultrasound is very sensitive for distinguishing whether a breast mass on breast examination or a mammogram is cystic (fluid-filled) or solid. Simple cysts are filled with clear fluid. Complex cysts have cloudy fluid mixed with debris and cells and can be difficult to distinguish from solid masses on ultrasound. Small asymptomatic cysts dont
require any treatment. Cysts which are painful or large enough to make breast examination difficult can be aspirated: under ultrasound guidance a thin needle is inserted into the cyst and the cyst fluid is withdrawn (ultrasound-guided fine needle aspiration). Complex cysts are also aspirated to be sure they truly are cysts and not solid masses. It is rare for a cyst to be associated with breast cancer. If a cyst has bloody fluid or there is a solid mass within it, a biopsy may be recommended.