What is DCIS?

How cancer develops Back to top

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 they divide in an orderly and controlled way. If for some reason the process gets out of control, the cells will continue to divide and eventually develop into a lump. Doctors can tell if the cells are cancer by removing a small piece of tissue (biopsy) and examining the cells under a microscope.

Breast cancers usually start in the cells that line the ducts, which are the channels that carry milk to the nipple (see the diagram of the breast|).

If a cancer is left untreated, it can spread in the area where it first started. Sometimes cells break away from the original cancer (primary) and spread to other organs in the body.

DCIS Back to top

DCIS is the earliest possible form of breast cancer.

There are cancer cells lining the ducts but these cells are completely contained (in situ) in the ducts.  The cells haven’t broken through the walls of the duct or grown into (invaded) surrounding breast tissue. 

Because it’s non-invasive, DCIS cannot 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 such as pre-invasive or intraductal cancer are also used to describe DCIS.

Although DCIS needs to be treated, it isn’t a life-threatening condition. 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.

DCIS and invasive breast cancer Back to top

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 always treated. Different factors such as how the cells look when they’re examined under a microscope and how abnormal they are (the grade|) help indicate the risk of DCIS becoming invasive.

Having DCIS means you have a slightly higher risk of getting cancer elsewhere in the same breast or in your other breast. You’ll have regular mammograms| after your treatment.