A breast lump is a mass that develops in the breast. Breast lumps are commonly found in one breast but can appear in both. Some may be too small or too deep to be felt from the outside and may appear in imaging studies like mammogram and/or ultrasound. Others may be detectable from the outside during a self-examination or a physical examination by a doctor.

Breast lumps can be found at all ages. Girls who are beginning puberty will experience breast changes due to hormonal changes. Breasts will grow as the milk-producing glands and ducts develop. This process can make the breasts feel “lumpier.” These lumps will settle as she enters adulthood. Breast lumps can also be found in boys, especially during the teenage years, also due to hormonal changes. They too tend to disappear on their own.
 
Types of Lumps
There are many types of breast lumps. The most common include:

• Fibrocystic changes account for 40% of all breast lumps.
• Fibroadenoma makes up 7-10% of breast lumps.
• Other benign lumps (13-20% of breast lumps) include cysts (fluid-filled sacs), lipomas (fat masses), phyllodes, hyperplasia, and adenosis.
• Malignant growths make up 10% of breast lumps.

Sometimes a patient may think they feel a lump in their breasts that the doctor is not able to find from the physical examination or imaging studies. This occurs in 30% of women who think they feel a lump.
 
Causes

• Fibrocystic changes occur due to hormonal changes that accompany menstrual cycles. Usually the lumps can be found in both breasts and often do not have well-defined borders. The skin may be dimpled and the lumps are usually soft and moveable. Fibrocystic changes are often accompanied by other symptoms, such as pain or tenderness of the breasts, the lumps, or under the arms. Breasts may look and/or feel swollen. Symptoms worsen close to menstruation, but usually improve once periods start. Birth control pills can alleviate these symptoms, while hormone replacement therapy, usually prescribed after the removal of the ovaries or menopause, can cause more lumps to develop. Fibrocystic changes do not usually become cancer.
• Fibroadenoma is a non-cancerous tumor that is commonly found in women under the age of 30. The cause for it is unknown, but it is believed to be related to hormones as the incidence is higher in women who take birth control pills before the age of 20. In most women the lump disappears after menopause. The tumor feels round and has a smooth surface. It is movable, slightly hard, and not painful. It can be big or small and there can be one or multiple tumors in one or both breasts. When the cells of the fibroadenoma are normal or have not changed (atypia), it is called simple fibroadenoma and is not at risk of becoming malignant. If the cells begin to change, it is called complex fibroadenoma. This puts the patient at higher risk than a normal woman for developing breast cancer. A biopsy can reveal exactly what kind of cells make up the tumor.
• Fat necrosis and oil cysts in the breast can be found after impact to the breasts, an accident, surgery, or radiation of the chest, causing death of the fat cells in the breast and leading to adhesions and/or oil cysts, which can feel like lumps in the breast. The lump is usual round, not too hard, and is slightly movable. Some hurts and some do not. There is usually an indication for the development of these lumps and these do not develop into cancer.
• Fluid-filled cysts do not have definitive causes, but are thought to be related to hormones as they seem to develop with fibrocystic changes. They occur in the reproductive age and disappear with menopause. The cysts may be round or oval, may or may not hurt, are usually movable, feel like water balloons, can be of varying sizes, and do not usually develop into cancer. Rarely the walls of the cysts may develop abnormally and increase a woman’s risk of breast cancer.
• Phyllodes or phylloids are rare, but when they occur are found in women of all ages, though most common between the ages of 30 and 40. The cause is unknown and the characteristics are like those of the fibroadenoma. Rarely do phyllodes become cancer (5%), but they have a high recurrence rate if removed surgically.
• Lipoma are fat lumps that develop without a clear cause, thought it is believed to be related to genetics. They usually have clear edges, are quite round, are soft, and do not often hurt. They are movable, but do not change in shape with menstruation. They do not develop into breast cancer, but rarely can develop into liposarcoma.
• Intraductal papilloma develops in the milk duct. It usually occurs in one breast, but can sometimes be found in both. The lump is not usually palpable, but if it is quite large, can be felt under the nipple. The patient may notice milk, blood, or other discharge leaking from the nipple. Sometimes this lump can develop into cancer, but it is rare.
• Duct ectasia develops when the milk duct is large and its walls are thicker than normal, forming a lump that is palpable under the skin. The lump is usually not too hard and is under the nipple. The nipple may become inverted and may leak a green or black discharge. It usually occurs in one breast. This lump does not develop into cancer.
• Adenosis develops when the milk duct expands and there are more milk ducts than normal. It occurs in one breast, but may be found in both. It may be felt under the skin and is not usually hard. If hard, it is sometimes due to sclerosing adenosis and can cause the breast to become misshapen. This lump does not usually become cancer, but if there are a lot of adhesions, the risk of breast cancer can go up.
• Mastitis or an abscess usually develops when a woman is breastfeeding and is caused by a bacterial infection. It is accompanied by a fever, swelling, redness, warmth, and pain. An abscess if usually obvious and may leak discharge from the nipple. This can occur in one breast or both. This does not usually develop into cancer, but some breast cancers can cause the same symptoms. The doctor will ask you about your medical history and decide whether a biopsy is needed to diagnose the problem.
• Hyperplasia is a term for all growths due to abnormal growth of cells. The doctor will be able to diagnose this through a biopsy where the cells are collected and looked at in the laboratory. Too many abnormal cells can be at risk of becoming breast cancer. If there is a mix of abnormal growth and abnormal cells, the risk of cancer is even higher.