Ductal carcinoma in situ (DCIS) is an early form of breast cancer. It may be described as a pre-cancerous, pre-invasive, non-invasive or intraductal cancer. This means the cancer cells are inside the milk ducts or ‘in situ’ (in place) and have not developed the ability to spread either within or outside the breast.

Most women with DCIS have no signs or symptoms so it is mostly found through breast screening after having a mammogram. This is why DCIS has been diagnosed more frequently since three-yearly breast screening was introduced on the UK National Health Service for women aged over 50. One in every thousand women who attend for breast screening is diagnosed with DCIS (NHS Breast Screening Programme 2015). The mammogram shows a cluster of small white dots. These white dots contain calcium and are known as micro-calcifications. They are generally too small to be felt. Most micro-calcifications turn out not to be DCIS (see ‘Benign breast problems‘).

A few women with DCIS do have symptoms. They may have a lump, a discharge from the nipple or, rarely, a type of rash involving the nipple called Paget’s disease.

If DCIS is left untreated, it may, over a period of years, begin to spread into (invade) the breast tissue surrounding the ducts. It is then known as invasive breast cancer. DCIS is the most common kind of non-invasive breast cancer; there are different grades of it’ low, intermediate and high. This grading is based on what the cells look like under the microscope. Low-grade DCIS has the lowest risk of developing into invasive cancer and high-grade the greatest risk.

DCIS is not harmful in itself, but it is usually treated to prevent it developing into an invasive breast cancer. Not every woman with DCIS will go on to develop breast cancer if it is left untreated, but it is not possible to predict reliably which women with DCIS will go on to develop invasive breast cancer. Treatment, usually surgical removal of the affected area(s) of the breast, aims to prevent the development of invasive cancer. For most women this will mean removing only a small part of the breast (lumpectomy or wide local excision). However, about three out of ten women (30%)* diagnosed with DCIS in the UK have their whole breast removed (mastectomy) because more than one part of the breast is affected.

In the UK, non-invasive cancers such as DCIS accounts for one in five cancers (20%) detected by screening; that’s around two thousand women a year (NHS Breast Screening Programme – Helping you decide leaflet July 2013). Health professionals haven’t yet reached a consensus about the nature of this disease and its management, although research is underway to inform this. Because DCIS has an uncertain natural progression, most women we spoke with found it hard to understand. None of the women we interviewed who had had DCIS had heard of it before. Many were confused as to whether it was actually cancerous or not. Most wanted more information about DCIS and many felt unprepared for the diagnosis because they’d had no symptoms.

See more about women’s experiences of DCIS.

*NHS Breast Screening Programme- Uncertainties in the management of screen-detected ductal carcinoma in situ July 2008.