A fibroadenoma of the breast is a common benign growth of the breast, often affecting young women. The cause is usually unknown, but it may be the result of an injury to the breast. It is possible to feel one or more round, firm (but not hard) lumps within the breast tissue that are hard to catch hold of and tend to slide out from between the fingers when squeezed (thus sometimes known as a breast mouse) and are therefore not attached to surrounding tissue. They are not usually tender or painful.
Mammography (breast x-ray) and ultrasound may be used initially, but in most cases a needle biopsy is necessary to confirm the diagnosis. If the diagnosis is confirmed to be benign, they may be left untreated, but if there is any doubt, they should be surgically removed. They persist long term if not removed.