by Jason Wasserman MD PhD FRCPC
March 4, 2022
Ductal carcinoma in situ (DCIS) is a non-invasive type of breast cancer. The tumour starts from specialized epithelial cells in the glands and ducts of the breast. DCIS is called non-invasive because, after careful microscopic examination, cancer cells were found only on the inside of the ducts and glands. If left untreated, patients with DCIS are at high risk for developing a more serious disease called invasive ductal carcinoma.
The diagnosis of DCIS is usually made after a small sample of breast tissue is removed in a procedure called a core needle biopsy. The biopsy is then examined under a microscope by a pathologist. Surgery may later be performed to remove the entire tumour which is sent to a pathologist for examination. Depending on the amount of breast tissue removed, the procedure may be called a ‘lumpectomy’ or a ‘mastectomy’.
Your pathologist will carefully examine the tissue under the microscope to see where the tumour cells are located within the breast. In order to make the diagnosis of DCIS, all of the tumour cells must be located inside the ducts. This is important because if any tumour cells are found outside of the ducts, the diagnosis changes to invasive ductal carcinoma.
Pathologists divide DCIS into three levels or grades – 1, 2, and 3. Instead of a numerical grade, some pathology reports divide the grade into low, intermediate, and high. Pathologists determine the grade for DCIS by looking at a part of the cell called the nucleus and comparing it to the cells normally found in the breast. Pathologists also look for the number of mitotic figures (tumour cells dividing to create new tumour cells). In general, grade 1 (low grade) DCIS is made up of cells that have small, round nuclei and few mitotic figures. In contrast, grade 3 (high grade) DCIS is made up of cells that have large, hyperchromatic (dark), and very irregularly shaped nuclei and mitotic figures are usually easy to find.
The nuclear grade is important because grade 3 (high grade) ductal carcinoma in situ is associated with a higher risk of developing invasive cancer compared to grade 1 (low grade) ductal carcinoma in situ.
Necrosis is a type of cell death. Comedonecrosis is a special type of necrosis sometimes seen in DCIS. In comedonecrosis, the dead cells are in the centre of a duct and surrounded by living cells. Comedonecrosis is more likely to be seen in high-grade ductal carcinoma in situ. It is also associated with an increased risk of cancer compared to ductal carcinoma in situ without comedonecrosis.
Estrogen receptor (ER) and progesterone receptor (PR) are proteins made by normal breast cells which allow the cells to respond to the hormones estrogen and progesterone. Your pathologist will perform a test called immunohistochemistry to see if the tumour cells make ER or PR. Tumours that make ER or PR are described as hormone positive. Tumours that do not make ER or PR are described as hormone negative.
Tumours that make ER or PR are treated with special medication that targets the activity of these proteins. After reviewing your pathology report, your doctor will talk with you about the treatment options best suited for you.
A margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. Whenever possible, surgeons will try to cut tissue outside of the tumour to reduce the risk that any cancer cells will be left behind after the tumour is removed.
Your pathologist will carefully examine all the margins in your tissue sample to see how close the cancer cells are to the edge of the cut tissue. Margins will only be described in your report after the entire tumour has been removed.
A negative margin means there were no cancer cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest cancer cells were to a margin. The distance is usually described in millimetres. A margin is considered positive when there are cancer cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will grow back (recur) in the same site after treatment.
If you received treatment (either chemotherapy or radiation therapy) for your cancer prior to the tumour being removed, your pathologist will examine all of the tissue submitted to see how much of the tumour is still alive (viable). Lymph nodes with cancer cells will also be examined for treatment effects.
The treatment effect will be reported as follows:
Lymph nodes are small immune organs located throughout the body. Cancer cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour. The movement of cancer cells from the tumour to a lymph node is called metastasis.
Lymph nodes are not always removed for ductal carcinoma in situ. However, if lymph nodes are removed, each lymph node will be carefully examined for cancer cells. Lymph nodes that contain cancer cells are often called positive while those that do not contain any cancer cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain cancer cells.
There are three types of lymph nodes that may be described in your report:
If cancer cells are found in a lymph node, the size of the area involved by cancer will be measured and described in your report as follows:
Finding cancer cells in a lymph node is associated with an increased risk that cancer will come back at a distant body site such as the lungs in the future. This information is also used to determine the nodal stage (see Pathologic stage below).
The pathologic stage for ductal carcinoma in situ is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer. This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M) to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and a worse prognosis.
Because ductal carcinoma in situ is a non-invasive form of cancer and is always given the tumour stage pTis.
Ductal carcinoma in situ is a non-invasive type of cancer. For this reason, it is very rare to find cancer cells in a lymph node. However, if cancer cells are found in one or more lymph nodes your pathologist will provide a nodal stage between 0 and 3 based on the number of lymph nodes that contain cancer cells, the number of cancer cells found in the lymph node, and the location of the lymph nodes with cancer cells.
Ductal carcinoma in situ is given a metastatic stage of 0 or 1 based on the presence of cancer cells at a distant site in the body (for example the lungs). Because ductal carcinoma in situ is a non-invasive type of cancer. For this reason, it is very rare to find cancer cells in another part of the body. The metastatic stage can only be determined if tissue from a distant site is submitted for pathological examination. Because this tissue is rarely sent, the metastatic stage cannot be determined and is listed as pMX.