Ductal carcinoma in situ (DCIS)
Ductal carcinoma in situ (DCIS) is the name for abnormal changes in the cells that line the milk ducts of the breast. While the abnormal cells may look similar to cancer cells under a microscope, they are precancerous cells that are contained within the milk ducts of the breast (in situ) and have not spread into surrounding breast tissue or to other parts of the body.
The abnormal cells remain in the milk ducts as they have not yet developed the ability to spread outside the ducts. As a result of being confined to the ducts, DCIS has a very good chance of cure.
DCIS is not invasive breast cancer. It is when precancerous cells are seen in the breast. DCIS is called non-invasive breast cancer because the abnormal cells are still inside the duct and have not grown into, or invaded, the normal breast tissue. DCIS is not life-threatening, but it can mean you are at higher risk of developing invasive breast cancer at a later time.
If DCIS is left untreated, it can spread outside the ducts into surrounding breast tissue and then potentially to other parts of the body. When this happens, it is called invasive breast cancer.
In Australia, it estimated that more than 2,000 women are diagnosed with DCIS every year, with most cases of DCIS being detected through screening mammograms.
To understand how DCIS develops it is helpful to understand what the breast looks like on the inside.
Women’s breasts are made up of a type of tissue called ‘glandular tissue’. This tissue has ducts and lobules supported by fibrous and fatty connective tissue (Figure 1 below).
There are around 12-15 major ducts in each breast that come together to drain into the nipple. Ducts and lobules are lined by two layers of cells:
The inside layer of cells called luminal epithelial cells, make milk during pregnancy.
The outer layer of cells, called myoepithelial cells, help push milk to the nipple during breast feeding.
Hormones produced by the body such as oestrogen and progesterone stimulate the glandular cells in the breast to grow at different times during a woman’s hormonal cycle, to prepare the breast cells for a possible pregnancy.
Sometimes cells lining the milk ducts in the breast can change into abnormal cells. This is a complex process and not fully understood.
Overtime, hormones being released in the body during women’s monthly cycles can lead to proliferative (growth) non-cancerous changes in the cells that line the breast ducts. These cell changes are called hyperplasia (an increase in the number of normal cells). Some of these changes may go on to become atypical hyperplasia (an excessive growth of cells that now have an abnormal appearance) and DCIS (an excessive growth of cells that look like cancer cells, confined to the inside of the duct).
When DCIS breaks through the ducts into the surrounding tissue, it is called invasive carcinoma (commonly referred to as invasive breast cancer). It is only then that it can spread to other parts of the body.
Figure 2 (below) shows how the cells of the milk ducts can change from normal cells to cancer cells. There is a spectrum of changes from benign(non-cancerous) to malignant (cancerous) cells in the breast. The timing, and rate, of how this change progresses differs from person to person. In any one person, different ducts may be at different stages of change. There may be no invasive breast cancer present, or there may be a mixture of DCIS and invasive breast cancer.
Depending on the timing and type of procedure performed (e.g. mammography followed by biopsy), it is sometimes hard to say accurately at what stage the cells are. Surgery is often needed to remove the area of DCIS. This surgery, combined with the pathology report, will determine the extent and level of disease that is present and provide a clear diagnosis.