The ducts of the breast are lined with two layers of cells. When these cells multiply abnormally, cancer cells in the duct can develop. Cancer in the duct is called ductal carcinoma in situ (DCIS). As long as the cancer cells stay inside the duct, DCIS has no risk of spreading. How long the cancer cells will stay contained in the ducts before they break through the duct wall and spread is a topic of considerable discussion among breast experts.

Not all DCIS is the same as it is a spectrum of disease. A biopsy lab report with DCIS will describe features which will help your doctors determine where on this spectrum the DCIS is located, which may impact treatment options.

The grading system of cancer cells looks at three features to determine a “grade” from minimally aggressive (low grade) to more aggressive (high grade). They look at the architecture of the cells, the shape and size of the nucleus of the cell, and the rate of cell division. A number from 1 to 3 is assigned to each category and added up. Those with the lowest points are grade 1/low grade whereas those with the most points are grade 3/high grade.

Estrogen and progesterone are the female hormones that are known to play a role in encouraging some breast cancer cells to grow and divide. When these cancer cells have the receptors to attract and bind to estrogen or progesterone, we refer to the cancer as an estrogen receptor (ER) or progesterone receptor (PR) positive cancer.

Grade 3 or even Grade 2 DCIS is a more aggressive form of DCIS. The most aggressive forms of DCIS may already be associated with “microinvasion”, very small areas that show movement of these cells out of the duct and into the surrounding breast tissue. Surgery is always recommended for these more aggressive forms.

Grade 1 DCIS is almost always ER and PR positive and is a very slow growing form of cancer. It can take years, even decades, to see progression of the disease. In some cases, it may take such a long time to spread beyond the breast duct that it is not an event that will happen during a person’s lifetime. However, surgical removal of these cancer cells is often recommended since we do not yet know how to predict which patient’s DCIS will progress if untreated.

But if the cells are so slow growing, why is any treatment necessary? The idea is to remove the cancer cells to prevent the cancer cells from returning in the future. If these cells reappear, about 50% will not come back as DCIS, but as an invasive cancer with the potential to metastasize (spread outside of the breast). Other treatments after surgery to lessen the chance that these cells return include radiation to the breast and medications to block the estrogen and progesterone receptors.

There are clinical trials that are looking at different ways to treat low grade DCIS. In these studies, women with low grade ER positive DCIS do not undergo surgery first, but receive medication to block the estrogen receptors. The patient’s area of cancer is watched very closely with imaging studies to make sure it is not growing. Surgery is recommended if the area appears to be growing. Some women on this trial have gone many years without needing surgery. It is a promising trial that is changing how we look at the spectrum of DCIS.