Breast lump - Causes of breast lumps

Most breast lumps are caused by benign (non-cancerous) conditions, although occasionally a breast lump can be a symptom of breast cancer.

It's important to see your GP as soon as possible if you notice a lump in your breast so they can refer you for tests to confirm the cause. Read more about diagnosing breast lumps.

Some of the main causes of breast lumps and their symptoms are outlined below.

Benign breast lumps

There are a number of different benign causes of breast lumps. Most benign breast lumps are harmless and may not necessarily require any treatment.

Fibroadenosis

Fibrocystic breast disease, also known as fibroadenosis, is a term used to describe a group of benign conditions that affect the breast. The symptoms of fibroadenosis can include:

breast pain (mastalgia or mastodynia)
increase in breast size
lumpiness of the breast (nodularity), particularly just before or during a period

Fibroadenosis can develop in one or both breasts, or can affect just part of one breast. The symptoms can also vary significantly between women, with some women finding them slightly annoying and others finding them very painful. The pain and lumpiness will usually disappear after your period.

The cause of fibroadenosis is not well understood. However, it may be the result of the breast tissue responding abnormally to hormonal changes that occur with the menstrual cycle.

Fibroadenomas

Fibroadenomas are smooth, well-rounded solid lumps of tissue that sometimes develop outside the milk ducts (the tiny tubes in the breast that carry milk). They are particularly common in young women.

They are sometimes described as "breast mice" because they can easily move around within the breast.

Fibroadenomas can disappear on their own, but they sometimes remain and grow larger, particularly during pregnancy. They don't usually resolve after your period.

It's not clear what causes fibroadenomas, but it is thought they may occur because of an abnormal response to the hormone oestrogen. This is because they are common in women who haven't been through the menopause and postmenopausal women who are having hormone replacement therapy (HRT).

Breast cysts

Breast cysts are fluid-filled sacs that develop within the breast tissue and can cause smooth, firm lumps to develop. They are more common in women aged 30 to 60.

Cysts vary in size. Some can be tiny, while others can grow to several centimetres in diameter. Single or multiple cysts can occur in one or both breasts.

Cysts often do not cause any symptoms, although some women may experience pain in addition to any lumps.

As with fibroadenomas, hormones are thought to play a role in the development of breast cysts because they are particularly common in pre-menopausal women and postmenopausal women having HRT.

Breast abscesses

A breast abscess is a painful collection of pus that forms inside the breast.

In addition to a painful lump, symptoms of a breast abscess can include a high temperature (fever) and inflammation (redness and swelling) of the skin over the affected area.

Most breast abscesses are caused by a bacterial infection. The bacteria usually enter the breast through small cracks or breaks in the skin of the nipple, which can sometimes develop during breastfeeding.

Other benign causes

Other benign causes of breast lumps include:

mastitis – where breast tissue becomes painful and inflamed
fat necrosis – a hard, irregular lump often caused by trauma or bruising to the breast; for example, after surgery on the breast
a lipoma – a fatty growth that causes a lump
an intraductal papilloma – a wart-like growth in a milk duct, which may also cause nipple discharge

Breast cancer

Although the vast majority of breast lumps are benign, a lump in one of the breasts can sometimes be a sign of breast cancer in women and breast cancer in men.

A lump is more likely to be a sign of breast cancer if it:

is clearly defined
feels firm
doesn't move around
persists after your period or develops after the menopause (in women)

Breast cancer can also cause some other symptoms, such as discharge from your nipples, dimpling on the skin of your breasts, and changes in the appearance of your nipple (such as becoming sunken into your breast).

The risk of breast cancer increases with age, but is most common in women and men over the age of 50. Having a family history of the condition may also mean your risk is increased.