Learn about your pathology report:

Undifferentiated pleomorphic sarcoma

What is undifferentiated pleomorphic sarcoma?

Undifferentiated pleomorphic sarcoma is a rare and aggressive type of cancer. It is part of a group of cancers called sarcomas. 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.

Dedifferentiation from a lower grade sarcoma

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.

How do pathologists make this diagnosis?

The diagnosis of undifferentiated pleomorphic sarcoma 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.

undifferentiated pleomorphic sarcoma

FNCLCC grade

Pathologists use the word grade to describe how different the cancer cells in undifferentiated pleomorphic sarcoma look and behave compared to normal, non-cancerous cells. The grade can only be determined after the tumour is examined under the microscope by your pathologist.

Undifferentiated pleomorphic sarcoma is given a grade based on an internationally recognized system created by the French Federation of Cancer Centers Sarcoma Group (FNCLCC).  According to this system, a tumour can receive a grade of 1 through 3. Grade 1 tumours are also called ‘low grade’ while grade 2 and 3 tumours are grouped together into a category called ‘high grade’. The FNCLCC grade is important because high-grade tumours are more aggressive tumours that are more likely to spread to other parts of the body or to re-grow after treatment.

Your pathologist will determine the FNCLCC grade of the tumour by looking for three microscopic features. Points are given to each feature (from 0 to 3) and the total number of points determines the final grade of the tumour.​

Features used to determine the FNCLCC grade:
  1. Tumour differentiation – Tumour differentiation describes how closely the cancer cells look like normal, non-cancerous cells. Tumours that look very similar to normal non-cancerous cells are given 1 point while those that look very different from normal non-cancerous cells are given 2 or 3 points. All undifferentiated pleomorphic sarcomas automatically receive 3 points for tumour differentiation.
  2. Mitotic count – A cell that is in the process of dividing to create two new cells is called a mitotic figure. Tumours that are growing fast tend to have more mitotic figures than tumours that are growing slowly. Your pathologist will determine the mitotic count by counting the number of mitotic figures in ten areas of the tumour while looking through the microscope. Tumours with no mitotic figure or very few mitotic figures are given 1 point while those with 10 to 20 mitotic figures are given 2 points and those with more than 20 mitotic figures are given 3 points.
  3. NecrosisNecrosis is a type of cell death. Tumours that are growing fast tend to have more necrosis than tumours that are growing slowly. If your pathologist sees no necrosis, the tumour will be given 0 points. The tumour will be given 1 point if necrosis is seen but it makes up less than 50% of the tumour or 2 points if necrosis makes more than 50% of the tumour.
Total points and grade:
  • Grade 1 – 2 or 3 points.
  • Grade 2 – 4 or 5 points.
  • Grade 3 – 6 to 8 points.
Molecular tests

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 a 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.

What to look for in your report after the tumour has been removed

Tumour size

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 the greatest dimension. Tumour size is important because it is used to determine the pathologic tumour stage (see Pathologic stage below). Tumours less than 5 cm are less likely to spread to other parts of the body and are associated with better prognosis.

Tumour extension​

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 bones. 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.

Treatment effect​

If you received chemotherapy and/or radiation therapy before the operation to remove the tumour, your pathologist will examine all the tissue sent to pathology to see how much of the tumour was still alive at the time it was removed from the body. Pathologists use the term viable to describe tissue that was still alive at the time it was removed from the body. In contrast, pathologists use the term non-viable to describe tissue that was not alive at the time it was removed from the body. Most commonly, your pathologist will describe the percentage of tumours that is non-viable.

Perineural invasion

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.

perineural invasion

Lymphovascular invasion

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.

lymphovascular invasion

Margins

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 negative margin means that no tumour cells were seen at any of the cut edges of tissue. 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.

Margin

Lymph nodes​

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 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.

Lymph node

Pathologic stage

​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 a worse prognosis.

Tumour stage (pT) for undifferentiated pleomorphic sarcoma

The tumour stage for undifferentiated pleomorphic sarcoma varies based on the body part involved. For example, a 5 centimetre 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.

Head and neck
  • T1 – The tumour is no greater than 2 centimetres in size.
  • T2 – The tumour is between 2 and 4 centimetres in size.
  • T3 – The tumour is greater than 4 centimetres in size.
  • T4 – The tumour has grown into surrounding tissues such as the bones of the face or skull, the eye, the larger blood vessels in the neck, or the brain.
Chest, back, or stomach and the arms or legs (trunk and extremities)
  • T1 – The tumour is no greater than 5 centimetres in size.
  • T2 – The tumour is between 5 and 10 centimetres in size.
  • T3 – The tumour is between 10 and 15 centimetres in size.
  • T4 – The tumour is greater than 15 centimetres in size.
Abdomen and organs inside the chest (thoracic visceral organs)
  • T1 – The tumour is only seen in one organ.
  • T2 – The tumour has grown into the connective tissue that surrounds the organ from which is started.
  • T3 – The tumour has grown into at least one other organ.
  • T4 – Multiple tumours are found.
Retroperitoneum (the space at the very back of the abdominal cavity)
  • T1 – The tumour is no greater than 5 centimetres in size.
  • T2 – The tumour is between 5 and 10 centimetres in size.
  • T3 – The tumour is between 10 and 15 centimeters in size.
  • T4 – The tumour is greater than 15 centimetres in size.
Tissue around the eye (orbit)
  • T1 – The tumour is no greater than 2 centimetres in size.
  • T2 – The tumour is greater than 2 centimeters in size but has not grown into the bones surrounding the eye.
  • T3 – The tumour has grown into the bones surrounding the eye or other bones of the skull.
  • T4 – The tumour has grown into the eye (the globe) or the surrounding tissues such as the eyelids, sinuses, or brain.
Nodal stage (pN) for undifferentiated pleomorphic sarcoma

Undifferentiated pleomorphic sarcoma is given a 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.

Metastasis stage (pM) for undifferentiated pleomorphic sarcoma

Undifferentiated pleomorphic sarcoma 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 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.

by Bibianna Purgina MD FRCPC (updated September 17, 2021)
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