This article was last reviewed on November 12, 2019 by Jason Wasserman, MD PhD FRCPC
The normal breast
Adult breast tissue is made up of small structures called glands. Glands are organized into groups called lobules. Under certain conditions, these glands can produce milk, which is transported to the nipple by a series of small channels called ducts.
The inside of both glands and ducts is lined by specialized cells called epithelial cells which form a barrier called the epithelium. The tissue surrounding glands and ducts is called stroma and contains long, thin cells called fibroblasts.
What is invasive ductal carcinoma?
Invasive ductal carcinoma is a type of a breast cancer. The tumour starts from the epithelial cells in the glands and ducts of the breast.
Invasive ductal carcinoma often starts from a non-invasive type of cancer called ductal carcinoma in situ (DCIS). Ductal carcinoma in situ can be present for months or years before turning into invasive ductal carcinoma.
When examined under a microscope, the abnormal cells in ductal carcinoma in situ are found only inside the glands and ducts. In order to become invasive ductal carcinoma, the cancer cells have to break out of the glands and ducts and enter the stroma. The movement of cancer cells from the glands and ducts into the stroma below is called invasion.
Ductal carcinoma is commonly called ‘breast cancer’ although there are actually several types of cancer that fall within this category. Ductal carcinoma, however, is the most common type of breast cancer to affect women worldwide.
Genetic syndromes associated with invasive ductal carcinoma
Some genetic syndrome are also associated with an increased risk for developing invasive ductal carcinoma. If you or a family member have been diagnosed with breast and ovarian cancer syndrome (BRCA1 and BRCA2), Cowden syndrome (PTEN), Peutz Jegher syndrome (STK11), or Li-Fraumeni syndrome (p53), you should talk with your doctor about your risk for developing breast cancer.
How do pathologists make this diagnosis?
The diagnosis of ductal carcinoma is usually made after a small sample of tissue is removed in a procedure called a biopsy. Surgery is then performed to remove the entire tumour which is sent to a pathologist for examination under the microscope.
Depending on the amount of breast tissue removed, the surgery performed may be called a ‘lumpectomy’ (which means removal of the ‘lump’) or a ‘mastectomy’ which means removal of the entire breast.
This is the size of the tumour measured in millimeters (mm). Tumour size will only be described in your report after the entire tumour has been removed. The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 40 mm by 20 mm by 15 mm, your report will describe the tumour as being 40 mm.
A tumour measuring 1 mm or less is usually called microinvasive.
Only the invasive part of the tumour is included in the size.
Why is this important? The tumour size is used to determine the tumour stage (see Pathologic stage below) and larger tumours are associated with worse prognosis.
Histologic grade (Nottingham or Scarff-Bloom-Richardson grading system)
The grade can only be determined after the tumour has been examined under the microscope. Your pathologist will look for the following three microscopic features to determine the grade.
The score from each category is added to determine the overall histologic grade as follows:
Why is this important? Compared to low grade tumours (grades 1 and 2), high grade tumours (grade 3) are associated with worse prognosis.
If more than one tumour is seen in your tissue, each will be described separately. The tumour stage (see Pathologic stage below) is based on the largest tumour found.
Ductal carcinoma starts inside the breast but the tumour may spread into the overlying skin or the muscles of the chest wall. The term tumour extension is used when cancer cells are found in either the skin or the muscles below the breast.
Why is this important? Tumour extension increases the tumour stage (see Pathologic stage below). It is also associated with a higher risk that the tumour will grow back after treatment (local recurrence) or that cancer cells will travel (metastasize) to a distant body site such as the lung.
Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through lymphatic channels.
Cancer cells can use blood vessels and lymphatics to travel away from the tumour to other parts of the body. The movement of cancer cells from the tumour to another part of the body is called metastasis.
Before cancer cells can metastasize, they need to enter a blood vessel or lymphatic. This is called lymphovascular invasion.
Why is this important? Lymphovascular invasion increases the risk that cancer cells will be found in a lymph node or a distant part of the body such as the lungs.
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 margin is considered positive when there are cancer cells at the very edge of the cut tissue. If ductal carcinoma in situ (DCIS) is seen at the edge of the cut tissue that will also be described in your report.
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 millimeters.
Why is this important? A positive margin is associated with a higher risk that the tumour will grow back in the same site after treatment (local recurrence).
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).
The treatment effect will be reported as follows:
Lymph nodes with cancer cells will also be examined for treatment effect.
Estrogen receptor (ER), progesterone receptor (PR), and HER2 status
Estrogen and progesterone receptors are proteins that are produced by normal breast cells which allow the cells to respond to the hormones estrogen and progesterone. HER2 is a special type of protein that allows cancer cells to grow faster than normal cells.
Your pathologist will test your tumour to see if it makes ER, PR or HER2. Tumours that make ER or PR are said to be hormone positive while those that make HER2 are called HER2 positive.
Tumours that do not make any of these proteins are called triple negative.
Why is this important? Tumours that make ER, PR, or HER2 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.
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 (see Lymphovascular invasion above). The movement of cancer cells from the tumour to a lymph node is called a metastasis.
Your pathologist will carefully examine each lymph node 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:
Why is this important? Finding cancer cells in a lymph node is associated with an increased risk that the 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 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 worse prognosis.
Tumour stage (pT) for invasive ductal carcinoma
Ductal carcinoma is given a tumour stage between 1 and 4 based on the size of the tumour and the presence of cancer cells in the skin or muscles of the chest wall.
Nodal stage (pN) for invasive ductal carcinoma
Ductal carcinoma is given a nodal stage between 0 and 3 based on the number of lymph nodes that contain cancer cells, the amount of cancer cells found in the lymph node, and the location of the lymph nodes with cancer cells.
If no lymph nodes are sent for pathological examination, the nodal stage cannot be determined and the nodal stage is listed as pNX.
Metastatic stage (pM) for invasive ductal carcinoma
Ductal carcinoma 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). 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.