What is DCIS?

Ductal carcinoma in situ (DCIS) is the earliest possible form of breast cancer. It needs to be treated but is not life-threatening.

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 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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Breast cancers usually start in the cells that line the lobules and their draining milk ducts. The place where DCIS starts is the terminal duct lobular unit.

In DCIS, the cancer cells are completely contained in the lobules and ducts. The cells haven’t broken through the walls of the lobules or ducts or grown into surrounding breast tissue.

Side view of the breast showing DCIS
Side view of the breast showing DCIS

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DCIS is the earliest possible form of breast cancer. It isn’t a life-threatening condition, but treatment is usually recommended.

DCIS and invasive breast cancer

If DCIS isn’t treated, it may over time spread into (invade) the breast tissue surrounding the ducts to become an invasive breast cancer. Not every untreated DCIS will develop into an invasive breast cancer. But breast specialists may advise treating DCIS because it isn’t possible to tell for certain which individual cases of DCIS will become an invasive cancer.

Having DCIS means you have a slightly higher risk of getting cancer elsewhere in the same breast or in your other breast. Guidelines recommend that women who have had DCIS have mammograms every year.

Back to Understanding DCIS

The breasts

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

Signs and symptoms of DCIS

Most women with DCIS have no symptoms and are diagnosed through NHS Breast Screening Programmes. A small number of women do have symptoms.