by Emily Goebel, MD FRCPC
June 2, 2022
Squamous cell carcinoma (SCC) is a type of cancer that starts from the skin on the surface of the vulva. In many cases, squamous cell carcinoma in the vulva develops from one of two pre-cancerous diseases: high grade squamous intraepithelial lesion (HSIL) or differentiated vulvar intraepithelial neoplasia (dVIN).
The diagnosis of squamous cell carcinoma is usually made after a small tissue sample is removed in a procedure called a biopsy. The entire tumour is usually then removed in a procedure called an excision or resection.
Pathologists use the term differentiated to divide squamous cell carcinoma of the vulva into three grades – well-differentiated, moderately differentiated, and poorly differentiated. The grade is based on how much the tumour cells look like normal squamous cells. A well-differentiated tumour (grade 1) is made up of tumour cells that look almost the same as normal squamous cells. A moderately differentiated tumour (grade 2) is made up of tumour cells that clearly look different from normal squamous cells, however, they can still be recognized as squamous cells. A poorly differentiated tumour (grade 3) is made up of tumour cells that look very little like normal squamous cells. These cells can look so abnormal that your pathologist may need to order an additional test such as immunohistochemistry to confirm the diagnosis. The grade is important because less differentiated tumours (moderately and poorly differentiated tumours) behave in a more aggressive manner and are more likely to spread to other parts of the body.
After the entire tumour has been removed, your pathologist will measure it in three dimensions and the largest dimension will be described in your pathology report. The size of the tumour is important because it is used to determine the pathologic tumour stage (pT).
Squamous cell carcinoma of the vulva starts in a thin layer of tissue on the surface of the vulva called the epidermis. Depth of invasion is a measurement of how far the tumour cells have spread from the epidermis into the layers of tissue below (the dermis and subcutaneous tissue). For vulvar tumours, the depth of invasion is measured from the surface of the skin to the deepest point of invasion. Some pathology reports describe the depth of invasion as tumour thickness. Tumours that grow deeper into the dermis are more likely to spread to a lymph node or to grow back 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. The term lymphovascular invasion is used to describe tumour cells that are found inside a blood vessel or lymphatic channel. Lymphovascular invasion is important because once the tumour cells are inside a blood vessel or lymphatic channel they are able to metastasize (spread) to other parts of the body such as lymph nodes or 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 tumour 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 tumour cells are to the edge of the cut tissue. Margins will only be described in your report after most or all of the tumour has been removed.
A negative margin means there were no tumour cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest tumour cells were to a margin. The distance is usually described in millimetres. A margin is considered positive when there are tumour cells at the very edge of the cut tissue. If HSIL or dVIN are seen at the margin that will also be described in your report. A positive margin increases the risk that the tumour will grow back in that location.
Lymph nodes are small immune organs located throughout the body. Tumour cells can spread from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of tumour cells from the tumour to a lymph node is called lymph node metastasis.
Lymph nodes are not typically removed for squamous cell carcinoma of the skin. However, if lymph nodes are removed your pathologist will carefully examine each one of them for tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells. The examination of lymph nodes is used to determine the pathologic nodal stage (pN).
A group of tumour cells inside of a lymph node is called a tumour deposit. If a tumour deposit is found, your pathologist will measure the deposit and the largest tumour deposit found will be described in your report. The largest tumour deposit is used to determine the pathologic nodal stage (pN). Larger tumour deposits are associated with a worse prognosis.
The pathologic stage for squamous cell carcinoma of the vulva 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.
Squamous cell carcinoma is given a tumour stage between 1 and 3. Your pathologist will look for three features in order to determine the tumour stage:
1. The size of the tumour.
2. Depth of invasion.
3. Tumor extension into nearby tissues including the urethra, vagina, bladder or rectum.
Squamous cell carcinoma is given a nodal stage of 0 or 3 based on the number of lymph nodes with tumour cells and the size of the largest tumour deposit in the lymph node. If no tumour cells are seen in any of the lymph nodes examined, the nodal stage is N0. Lymph nodes with isolated tumour cells are also given a nodal stage of N0. If no lymph nodes are submitted for pathological examination, the nodal stage cannot be determined and the nodal stage is listed as NX.
Metastatic stage (pM) for squamous cell carcinoma of the vulva
Squamous cell carcinoma is given a metastatic stage of 0 or 1 based on the presence of tumour cells at a distant site in the body (for example the lungs). The metastatic stage can only be assigned 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 MX.