Ductal carcinoma in situ (DCIS) of the breast

by Jason Wasserman MD PhD FRCPC
March 9, 2023

What is ductal carcinoma in situ?

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.

Is ductal carcinoma in situ a type of cancer?

Yes. DCIS is a non-invasive type of breast cancer. It is called non-invasive because the tumour cells have not spread beyond the ducts and glands into the surrounding breast tissue.

How is ductal carcinoma in situ diagnosed?

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.

What does nuclear grade mean and why is it important?

Pathologists divide DCIS into three levels or grades – grade 1 (low),  grade 2 (intermediate), and grade 3 (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).

• Ductal carcinoma in situ, grade 1, low grade – These tumours have a low nuclear grade and relatively few mitotic figures.
• Ductal carcinoma in situ, grade 2, intermediate grade – These tumours have an intermediate nuclear grade and a small number of mitotic figures.
• Ductal carcinoma in situ, grade 3, high grade – These tumours have a high nuclear grade and mitotic figures are found throughout the tumour.

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.

What does comedonecrosis mean?

Comedonerosis is a term that describes dead tumour cells in the centre of a duct. It is more likely to be seen in grade 3 (high grade) ductal carcinoma in situ. It is also associated with an increased risk of invasive ductal carcinoma compared to ductal carcinoma in situ without comedonecrosis.​​

What are estrogen receptor (ER) and progesterone receptor (PR) and why are they important?​​

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. The tumour cells in DCIS can also make ER and PR which allows the tumour cells to grow in response to these hormones.

Your pathologist may 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.

The ER and PR status of a tumour is important because tumours that make ER or PR are treated with a 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.

What is a margin and why it important?

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.

What stage is ductal carcinoma in situ?

Because ductal carcinoma in situ is a non-invasive form of cancer and is always given the pathologic tumour stage pTis.