What is DCIS?

Ductal carcinoma in situ, or DCIS for short, is the earliest form of breast cancer. Although DCIS needs to be treated, it isn’t a life-threatening condition.

Breast cancers usually start in the cells that line the lobes and milk ducts. In DCIS, there are cancer cells lining the ducts but they are completely contained in the ducts. They haven’t started to spread into the surrounding breast tissue. Before cancer cells develop the ability to spread, they are called non-invasive or in situ cancers. DCIS is one of these non-invasive cancers.

As DCIS is a very early form of breast cancer, women are usually diagnosed when they have a mammogram (breast x-ray) as part of the National Breast Screening Programme.

What is DCIS?

Ductal carcinoma in situ (DCIS) is the earliest possible form of breast cancer and is non-invasive. This means although there are breast cancer cells in the milk ducts (channels that carry milk), they are completely contained and haven’t spread into surrounding breast tissue.


How cancer develops

To understand DCIS, it helps to know how cancer usually develops.

The organs and tissues of the body are made up of tiny building blocks called cells. Normally, cells divide in an orderly and controlled way. But if for some reason the process gets out of control, the cells carry on dividing, and develop into a lump called a tumour. Doctors can tell whether a tumour is benign (non-cancerous) or malignant (cancerous) by removing a piece of tissue (biopsy) and examining a small sample of cells under a microscope.

Cells forming a tumour
Cells forming a tumour

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In a benign tumour, the cells do not spread to other parts of the body and so are not cancerous.

In a malignant tumour, the cancer cells have the ability to spread beyond the original area of the body. This is called an invasive tumour. If the tumour is left untreated, it may spread into surrounding tissue. Sometimes cells break away from the original (primary) cancer. They may spread to other organs in the body through the bloodstream or lymphatic system.

When the cancer cells reach a new area they may go on dividing and form a new tumour. This is known as a secondary cancer or a metastasis.

Before cancer cells develop the ability to spread they are called non-invasive or in situ cancers. Non-invasive cancers of the breast are usually of a type called ductal, and are known as ductal carcinoma in situ, (DCIS).


About DCIS

Although DCIS needs to be treated, it isn’t a life-threatening condition. It’s the earliest possible form of breast cancer.

Breast cancers usually start in the cells that line the lobes and milk ducts. In DCIS, there are cancer cells lining the ducts but they are completely contained in the ducts.

The cells haven’t broken through the walls of the duct or grown into surrounding breast tissue. Because it’s non-invasive, DCIS will not have spread to the lymph nodes under the arm, which is where invasive breast cancers can spread to, or to anywhere else in the body. Terms like pre-invasive or intraductal cancer are also used to describe DCIS.

DCIS is usually diagnosed when women have a mammogram (breast x-ray) as part of the National Breast Screening Programme. One in every thousand women in the UK who attends breast screening is diagnosed with DCIS. The number of cases is increasing because more women are being screened and mammograms have improved.


Back to Understanding DCIS

The breasts

Breasts are made up of fat, supportive (connective) tissue and glandular tissue containing milk lobes.

DCIS and invasive breast cancer

If ductal carcinoma in situ (DCIS) is not treated, it may spread into (invade) the breast tissue surrounding the ducts.

How is it treated?

There are five main types of cancer treatment. You may receive one, or a combination of treatments, depending on your cancer type.