This article will help you read and understand your pathology report for undifferentiated pleomorphic sarcoma.
by Bibianna Purgina MD FRCPC, updated January 7, 2021
Undifferentiated pleomorphic sarcoma is a rare and aggressive type of cancer. It is part of a group of cancers called sarcomas. 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 an undifferentiated pleomorphic sarcoma arises from is currently unknown. Most undifferentiated pleomorphic sarcomas occur in adults.
The cancers cells of undifferentiated pleomorphic sarcoma are called undifferentiated because they do not look like any normal type of cell when examined under the microscope. The word pleomorphic means that the cancer cells show a lot of variation in size and shape throughout the tumor.
Some less aggressive or lower grade sarcomas undergo a process called dedifferentiation. When this happens, the tumour cells change so they no longer look like cells normally found in the body. For example, when dedifferentiation happens in a sarcoma made up of fat cells, the tumour cells change so that they no longer look like fat.
The dedifferentiated area of a tumour can look like an undifferentiated pleomorphic sarcoma. For this reason it can be very difficult for a pathologist to tell the difference between an undifferentiated pleomorphic sarcoma and dedifferentiation of another type of sarcoma especially when only a small sample of tumour is examined. However, unlike dedifferentiated tumours, undifferentiated pleomorphic sarcoma does not develop from a less aggressive or lower grade tumour.
The diagnosis is often first suggested after a small sample of tumour is removed in a procedure called a biopsy. In the biopsy report your pathologist will provide your doctor with a list of possible diagnoses that includes an undifferentiated pleomorphic sarcoma and dedifferentiated sarcomas. Often a final diagnosis cannot be made until the whole tumour is surgically removed and the pathologist is able to examine the entire specimen.
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.
The grade based on an internationally recognized system created by the French Federation of Cancer Centers Sarcoma Group. According to this system, a tumour can receive a grade of 1 through 3.
If you have been diagnosed with an undifferentiated pleomorphic sarcoma, your pathologist will determine the French Federation of Cancer Centers Sarcoma Group grade of your 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, undifferentiated pleomorphic sarcomas are high grade tumors which always receive a grade of 2 or 3.
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.
Some sarcomas have characteristic changes to the tumour DNA that can be found using molecular tests. Unfortunately, at our current level of understanding, undifferentiated pleomorphic sarcoma does not have any known characteristic molecular changes.
Sometimes, your pathologist will perform molecular tests on your undifferentiated pleomorphic sarcoma to rule out other sarcomas. A negative molecular test (for example, a molecular test without an identified translocation or amplification) is consistent with an undifferentiated pleomorphic sarcoma.
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 more often done on the biopsy specimen. If your pathologist is certain that your tumor is an undifferentiated pleomorphic sarcoma, then no molecular testing may be done.
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 undifferentiated pleomorphic sarcomas tend to occur in deep sites such as the muscles of the thigh or the psoas muscle in the abdomen/retroperitoneum. Undifferentiated pleomorphic sarcoma can 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 contain 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 undifferentiated pleomorphic 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 undifferentiated pleomorphic 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.
The tumour stage for undifferentiated pleomorphic 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.
Undifferentiated pleomorphic 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.
Undifferentiated pleomorphic 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.