The Normal Breast

The female breast is made up of fat and milk glands. These glands are composed of basic units called lobules, and are drained by tubes (or ducts) that open at the nipple. The glandular part of the breast is in the middle and feels firmer than the surrounding fatty tissue (Image below).


The relative proportions of milk glands, ducts and fat in the breast change with a woman’s age and also during pregnancy. For example, the breast of a 25-year-old woman is mainly made up of milk glands, whereas, during pregnancy and breast-feeding, the number of milk glands increases substantially. The female sex hormone oestrogen acts on the breast to maintain the milk glands and ducts. During the menopause there is a decrease in the level of this hormone that causes the shrinkage of the glandular part of the breast. The glands are replaced by fat, which is why the breasts often feel softer after the menopause. Hormone replacement therapy helps to prevent these changes (see HRT).

The breast also contains special channels called lymphatic vessels. These vessels transport fluid that accumulates between the cells and return it back into the blood circulation. The lymphatic vessels connect with lymph glands (also called lymph nodes). These are located all over the body. Most of the lymph glands draining the breast are found in the armpit. Cancer cells can spread along lymph vessels and into the lymph glands, causing them to enlarge.

What is Breast Cancer?

The cell is the basic building block of the body, making up all of our tissues and organs. As cells grow old and wear out, new ones replace them. This process is called cell division, as is illustrated in the image below.


The balance between dying and growing cells is vital to maintain the normal functioning of our bodies. If the number of growing cells exceeds the number of dying cells, then a lump(or tumour) will develop. If the cells in the tumour divide haphazardly and grow in an aggressive manner, this is called a cancer or malignant tumour.

Malignant cells have the potential of invading adjacent tissues and can spread to other parts of the body some distance away from the main (or primary) tumour. This process of distant spread is called metastasis. It can occur through the blood stream or the lymph vessels.

A breast cancer occurs when the cells of the milk glands or the milk ducts grow and divide

in a disorderly manner. This may be detected as a lump in the breast. It can take months or years for a tumour of 1 cm in diameter to grow in the breast. It is estimated that a tumour of this size contains one billion breast cancer cells!

The appearance of breast cancer on a mammographic film after removal by lumpectomy

What are the main Types of Breast Cancer?

There are two main types of breast cancer: invasive and non-invasive

Type 1 – Invasive Breast Cancer

This cancer is more aggressive and has the ability to spread elsewhere in the body and thus cause death. It is called “ductal” if it arises from the milk ducts and “lobular” if it arises from the lobules of the milk glands

Type 2 – Non-invasive Breast Cancer

This type is confined to the ducts or lobules of the milk glands. It is a non-invasive cancer and does not usually spread to other parts of the body. However, it may develop into an invasive type if left untreated. The medical name for non-invasive breast cancer is ductal carcinoma in situ (DCIS) if it occurs in the milk gland ducts (tubes), or lobular carcinoma in situ (LCIS) if it occurs in the gland lobules.

LCIS is not considered as cancer as such. The presence of this abnormality in a breast biopsy means the patient has an increased risk of developing breast cancer. The risk means that about 1 in 3 women with LCIS will develop breast cancer within 30 years of being diagnosed with the original condition.

The risk of DCIS progessing to become invasive breast cancer varies between 25-85% depending upon the biological profile of DCIS.


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