How DCIS develops in the breast

Some changes in the breast are normal as we age because of the hormones people (especially women) produce.

DCIS can develop when changes in the lining of the milk ducts of the breast are abnormal.

DCIS is a complex condition but it is not invasive breast cancer.

Anatomy of the breast

To understand how DCIS develops, it is helpful to understand what the breast looks like on the inside.

Women’s breasts are made up of a type of tissue called ‘glandular tissue’.

This tissue has:

• lobules – glands that produce milk
• ducts – around 12 to 15 major tubes in each breast that carry milk to the nipple.

Two layers of cells line the ducts and lobules:

• An inside layer – luminal epithelial cells, which make milk during pregnancy.
• An outer layer – myoepithelial cells, which help push milk to the nipple during breast feeding.

Fibrous and fatty connective tissue supports the ducts and lobules.

At different times during a woman’s cycle, the body produces hormones such as oestrogen and progesterone. These encourage the glandular cells in the breast to grow, to prepare the breast cells for a possible pregnancy.

Normal changes in the breast

Hormones released in the body can lead to non-cancerous changes in the cells that line the breast ducts. These hormones are mostly (but not all) released during women’s monthly menstrual cycles, which is why DCIS is very rare in men.

The changes are called ‘fibrocystic’ changes. Fibro cystic changes are common, non-cancerous (‘benign’) and do not need any treatment. Medical names for such changes are cystic change, hyperplasia and metaplasia.

During a mammogram, these 'fibrocystic' changes are often picked up and can appear as white spots/shadows. Fibrous tissue often surrounds these cysts and the fluid in the cyst can harden due to deposits of calcium (‘calcification’).

Sometimes people can feel these cysts as a lump.

Precancerous changes in the milk ducts

Changes in the breast cells can range from non-cancerous (‘benign’) to cancerous (‘malignant’).

Normal cell changes are called hyperplasia – an increase in the number of normal cells.

Sometimes cells lining the milk ducts can change into abnormal cells. This is a complex process and not fully understood.

Some of these changes may go on to become:

• atypical hyperplasia – the excessive growth of cells that now have an abnormal appearance
• ductal carcinoma in situ (DCIS) – an excessive growth of cells that look like cancer cells, confined to the inside of the duct
• invasive carcinoma – if DCIS breaks through the ducts into the surrounding tissue, it can spread to other parts of the body and become invasive breast cancer.

The timing and the rate of change is different from person to person. One person may have different ducts at different stages of change. There may be:

• no invasive breast cancer present
• a mixture of DCIS and invasive breast cancer.

Doctors may ask for a mammography followed by a biopsy to accurately diagnose DCIS. Find out about Diagnosis of DCIS.

Surgery is often needed as treatment for DCIS, to remove the area of DCIS. From this, the pathology report will determine the type and extent of disease and provide a clear diagnosis.