It is harmless and frequently cannot be felt. In some cases the only symptom is a watery, pink discharge from the nipple. Since a watery or bloody discharge can be seen in cases of breast cancer, this must be evaluated by your physician. Cancer can cause a lump. A microscopic examination of the fluid, as well as a mammogram, is recommended to check this possibility.
Surgical removal is in most cases recommended.
Sometimes an injury to the breast will cause a bruise large enough to appear as a lump. The lump is actually a collection of blood in the traumatized area. There may be significant swelling and tenderness, but this should slowly return to normal over a few days or weeks. When necessary, it can be drained surgically but there is some risk of infection in doing so. Treatment of benign breast lumps varies with the situation.