Breast health

What is breast cancer?

Breast cancer, like other cancers, is a disease of the body's cells. Occasionally, some cells begin to behave in an abnormal way and grow into a mass of tissue called a tumour, or cancer.

Breast cancer generally arises in the cells that line the specialised glandular breast tissue. There are Breast cancer, some grow very slowly whilst others develop more rapidly.

Structure and function of the breast

The breasts (mammary glands) are a pair of organs that produce milk after pregnancy and are made up of glandular, fibrous and fatty tissues.

The glandular tissue, consisting of milk sacs and ducts, is divided into segments or lobes arranged like the spokes of a wheel. From each lobe the milk ducts lead to the nipple area (see diagram). The lobes of glandular tissue are surrounded by fatty and fibrous tissues.

In the breast area and the armpit, there are lymph glands or nodes which are connected by a system of channels. These glands and channels are part of the lymph system which helps the body fight infection.

Illustration of the breast reproduced with permission from Cancer Australia

Image reproduced with permission from Cancer Australia

Breast density

Breasts are made up partly of fat and partly of glands and fibrous, supporting tissue (together called fibroglandular tissue). While fat appears dark on a screening mammogram, fibroglandular tissue appears ‘dense’ or white.

Each woman’s breasts are different and contain a unique mix of fatty and dense tissue. For reasons that are not fully understood, some women will have lots of dense breast tissue, while others will have little.

A woman with lower breast density will have more fatty tissue, whereas a woman with higher breast density will have less fatty tissue.Dense breast tissue is common and normal, occurring in around one third of women aged over 50. It usually reduces with age. The images below show normal breasts with different densities.

an example female breast density - least dense an example female breast density - less dense an example female breast density - more dense an example female breast density - most dense
Least dense Less dense More dense Most dense


For more information on breast density, please see BreastScreen SA's position statements.

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