This article will help you read and understand your pathology report for synovial sarcoma.
by Bibianna Purgina MD FRCPC, updated January 7, 2021
Synovial sarcoma is a type of cancer called a sarcoma. Sarcomas are cancers that develop from mesenchymal tissues which include nerves, fat, muscle, blood vessels, tendons, ligaments, bone and cartilage. The type of mesenchymal tissue that a synovial sarcoma arises from is currently unknown.
Because the earliest reports of synovial sarcoma described tumours around joints such as the knee, the tumour was thought to develop from the tissue around the joint called synovium. We know now that the tumour does not actually develop from the synovium, however, the original name (“synovial”) still remains.
Synovial sarcoma can develop at any age but are most common in adults. Common locations include the arms and legs but the tumour can develop anywhere in the body.
Synovial sarcomas have a characteristic genetic change called a translocation. Usually the translocation in synovial sarcoma combines the gene SS18 with either SS1, SSX2 or SSX4 genes. These translocations can be found using molecular tests (see Molecular tests below).
There are two main types of synovial sarcoma: biphasic synovial sarcoma and monophasic synovial sarcoma. Other types of synovial sarcoma exist, including poorly differentiated synovial sarcoma, however, these are very rare.
The first diagnosis of synovial sarcoma is usually made after a small sample of the tumour is removed in a procedure called a biopsy. The biopsy tissue is then sent to a pathologist who examines it under a microscope. Additional tests such as immunohistochemistry and fluorescence in situ hybridization (FISH) may also be performed to confirm the diagnosis.
Under the microscope, biphasic synovial sarcomas are made of two types of cancer cells: epithelial tumor cells and spindle tumour cells. Monophasic synovial sarcomas are made of only one of these types of cancer cells, usually the spindle tumour cells.
After a pathologist makes a diagnosis of synovial sarcoma or suggests this as a possibility, the patient is usually treated first with surgery to remove the tumour. Sometimes, the patient may receive chemotherapy and/or radiation therapy before surgery, but usually these treatments are done after surgery, if recommended by your surgeon or oncologist. When the tumour is surgically removed as a resection specimen, it is sent to pathology for examination.
Features of synovial sarcoma that are associated with a worse prognosis include:
These features are described in greater detail in the sections below.
Grade is a word pathologists use to describe how different the cancer cells look and behave compared to normal cells in the same location. The grade can only be determined after the tumour is examined under the microscope by your pathologist.
Synovial sarcomas are given a grade based on an internationally recognized system created by the French Federation of Cancer Centers Sarcoma Group (FNCLCC). Pathologists determine the French Federation of Cancer Centers Sarcoma Group grade of a tumour by looking for three microscopic features:
The final grade is based on the total number of points given to the tumour:
According to this system, all synovial sarcomas are high grade tumors. High grade tumors are more likely to spread to other parts of the body and are associated with worse prognosis.
Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes and each gene tells the cell how to produce piece of the machine called a protein.
Sometimes, a piece of DNA falls off one chromosome and becomes attached to a different chromosome. This is called a translocation and it can result in the cell making a new and abnormal protein. If the new protein allows the cell to live longer than other cells or spread to other parts of the body, the cell can become a cancer (a malignant tumour).
Synovial sarcoma contains a translocation that combines the gene SS18 with either SS1, SSX2 or SSX4 genes. Tumours with the SS18-SSX1 translocation are associated with worse prognosis compared to tumours with translocations involving other genes.
Pathologists test for these molecular changes by performing either fluorescence in situ hybridization (FISH) or next generation sequencing (NGS) on a piece of the tissue from the tumour. This type of testing is can be done on the biopsy specimen or when your tumor has been surgically removed.
The tumour is measured in three dimensions but only the largest dimension is typically included in your report. For example, if the tumour measures 5.0 cm by 3.2 cm by 1.1 cm, the report may describe the tumour size as 5.0 cm in greatest dimension.
Tumour size is used to determine the pathologic stage. Tumours less than 5 cm are less likely to spread to other parts of the body and are associated with better prognosis.
Most synovial sarcomas tend to occur in the extremity are well defined, but may grow into or around organs and bone. Your pathologist will examine samples of the surrounding organs and tissues under the microscope to look for cancer cells. Any surrounding organs or tissue that contains cancer cells will be described in your report.
If you received chemotherapy and/or radiation therapy before the operation to remove your tumour, your pathologist will examine all the tissue sent to pathology to see how much of the tumour is still alive (viable). Most commonly, your pathologist will describe the percentage of tumour that is dead.
Nerves are like long wires made up of groups of cells called neurons. Nerves transmit information (such as temperature, pressure, and pain) between your brain and your body. Perineural invasion is a term pathologists use to describe cancer cells attached to a nerve.
Perineural invasion is important because cancer cells that have attached to a nerve can use the nerve to travel into tissue outside of the original tumour. For this reason, perineural invasion is associated with a higher risk that the tumour will come back in the same area of the body (local 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. Before cancer cells can metastasize, they need to enter a blood vessel or lymphatic. This is called lymphovascular invasion.
Lymphovascular invasion is important because it 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. The types of margins described in your report will depend on the organ involved and the type of surgery performed. Margins will only be described in your report after the entire tumour has been removed.
A margin is called positive when there are tumour cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment. A negative margin means that no tumour cells were seen at any of the cut edges of tissue.
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.
Many cancers can spread to the lymph nodes, but synovial sarcoma does this very rarely. If lymph nodes were part of the surgery to remove your tumour, your pathologist will assess them under the microscope and report whether they are involved by tumour.
The pathologic stage for synovial sarcoma 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 synovial sarcoma
The tumour stage for synovial sarcoma varies based on the body part involved. For example, a 5 centimeter tumour that starts in the head will be given a different tumour stage than a tumour that starts deep in the back of the abdomen (the retroperitoneum). However, in most body sites, the tumour stage includes the tumour size and whether the tumour has grown into surrounding body parts.
Synovial sarcoma is given an nodal stage of 0 or 1 based on the presence or absence of cancer cells in one or more lymph nodes.
If no cancer cells are seen in any lymph nodes, the nodal stage is N0. If no lymph nodes are sent for pathological examination, the nodal stage cannot be determined, and the nodal stage is listed as NX. If cancer cells are found in any lymph nodes, then the nodal stage is listed as N1.
Synovial sarcoma is given an 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 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.
The metastatic stage can only be given if tissue from a distant site is sent for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined, and it is typically not included in your report.