What is DCIS?
DCIS is non-invasive. This means that although there are breast cancer cells in the milk ducts, they are completely contained in this area and haven't spread into surrounding breast tissue.
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.
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 and spread to other organs in the body. 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 malignant cancer cells develop the ability to spread they are called non-invasive or in situ cancers. Non-invasive cancers of the breast are usually found in the milk ducts and are known as ductal carcinoma in situ (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 milk ducts but they are completely contained in the ducts. The cells haven’t broken through the walls of the ducts or grown into surrounding breast tissue.
When cancer starts in the lobes, it’s called lobular carcinoma in situ (LCIS), which is very different from DCIS. We have separate information about LCIS.
Because it’s non-invasive, DCIS cannot spread to the lymph nodes under the arm, which is where invasive breast cancers can sometimes spread. They can’t spread to anywhere else in the body either. Terms like ‘pre-invasive’ or ‘intraductal cancer’ are also used to describe DCIS.
DCIS is usually diagnosed when a woman has a mammogram (breast x-ray) as part of the NHS 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.
We have more information about how DCIS is diagnosed.
DCIS and invasive breast cancer
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If DCIS isn’t treated, it may develop the ability to spread into the breast tissue surrounding the ducts. If this happens, it’s no longer DCIS – it’s now an invasive breast cancer.
Not every woman with untreated DCIS will develop an invasive breast cancer. It isn’t possible to predict with any certainty when or in which women an invasive cancer will develop. This is why, if found, DCIS is usually always treated. Different factors such as how the cells look when they’re examined under a microscope and how abnormal they are (the grade) can help to indicate the risk of DCIS becoming invasive. We have more information about grading DCIS.
Having DCIS means you have a slightly higher risk of getting cancer elsewhere in the same breast or in your other breast. For this reason, it’s recommended that women with DCIS receive regular mammograms (every 1–2 years). We have more information about follow-up after DCIS.