This article will help you read and understand your pathology report for squamous cell carcinoma of the anal canal.
by Catherine Forse MD FRCPC, reviewed December 27, 2020
The anal canal is the last part of the gastrointestinal tract. It connects the rectum to the anus. The anus is the external opening where fecal matter is released from the body.
The anal canal is made up of 3 layers of tissue:
Squamous cell carcinoma in the anal canal is primarily caused by infection with the human papillomavirus (HPV).
Symptoms of squamous cell carcinoma in the anal canal may include bleeding from the anus, anal itching, anal pain or the ability to feel a lump around your anus.
The diagnosis is usually made after a small piece of the tumour is removed in a procedure called a biopsy. The tissue is sent to a pathologist for examination under a microscope. A special test called immunohistochemistry may be performed to confirm the diagnosis.
Patients are usually offered radiation or chemotherapy for treatment. For most patients, surgery is not required; however, in some situations surgery may be needed.
If surgery is performed, the entire tumour will be sent to a pathologist who will examine parts of it under the microscope. This report will confirm or revise the original diagnosis and provide additional important information such tumour size, extension, margins, and spread of tumour cells to lymph nodes. This information is used to determine the cancer stage and to decide if additional treatment is required.
Pathologists use the word grade to describe how different the cancer cells in squamous cell carcinoma look compared to the normal, healthy squamous cells found in the anal canal.
Pathologists divide the grade into three categories based on how the cancer cells look when examined under the microscope.
Grade is important because poorly differentiated tumours are more likely to spread to other parts of the body and to re-grow after treatment.
This is the size of the tumour. The tumour is usually measured in three dimensions but only the largest dimension may be described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.
The anal canal is a tube and the wall of the tube is made up of three to four different layers of tissue depending on the location in the anal canal (see above). Squamous cell carcinoma starts in the epithelium on the inner surface of the anal canal. The spread of cancer cells from the epithelium into the tissue below is called invasion. Tumour extension describes how far the cancer cells have spread from the epithelium into the layers of tissue below.
Your pathology report will describe the tumour extension as follows:
Although knowing the tumour extension is important, it is the tumour size which determines the pathologic tumour stage (see Pathologic stage below). Cancer cells that have spread further into the wall of the anal canal are more likely to come back after treatment in the area of the original tumour or spread to a distant site such as the lungs. The movement of cancer cells to another part of the body is called metastasis.
In your report, tumour site refers to whether the tumour is found in the anal canal, perianal region or another location.
Nerves are like long wires made up of groups of cells called neurons. Nerves send information (such as temperature, pressure, and pain) between your brain and your body. Perineural invasion means that cancer cells were seen attached to a nerve.
Cancer cells that have attached to a nerve can use the nerve to travel into tissue outside of the original tumour. This increases the risk that the tumour will re-grow in the same area of the body (recurrence) after treatment.
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.
When cancer cells enter a blood vessel or lymphatic, this is called lymphovascular invasion.
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.
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 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.
Finding cancer cells in a lymph node is associated with an increased risk that the cancer cells will spread to other parts of the body. The number of lymph nodes with cancer cells is also used to determine the nodal stage (see Pathologic stage below).
In the anal canal, a margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. The types of margins present will depend on the type of procedure that was performed.
For abdominoperineal resection (APR) specimens where the entire anal canal has been removed, the margins will include:
For endoscopic resections (transanal disk excisions) where only a small piece of the inside of the anal canal has been removed, the margins will include:
In the anal canal, 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 re-grow 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).
The treatment effect will be reported on a scale of 0 to 3 with 0 being no viable cancer cells (all the cancer cells are dead) and 3 being extensive residual cancer with no apparent regression of the tumour (all or most of the cancer cells are alive).
Lymph nodes with cancer cells will also be examined for treatment effect.
The pathologic stage for squamous cell 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.
Squamous cell carcinoma is given a tumour stage between 1 and 4 based on the size of the tumour.
Squamous cell carcinoma of the anal canal is given a nodal stage of 0 or 1. Nodal stage 1 is divided into 1a, 1b and 1c based on where the lymph nodes invaded by cancer cells are located in the body.
If no lymph nodes are submitted for pathological examination, the nodal stage cannot be determined and the nodal stage is listed as NX.
Squamous cell 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 present, the metastatic stage cannot be determined and is listed as X.