Learn about your pathology report:

Dedifferentiated liposarcoma

What is dedifferentiated liposarcoma?

Liposarcoma is a type of cancer made up of abnormal fat cells. 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. Dedifferentiated liposarcoma is an aggressive type of cancer that develops from another type of liposarcoma called well-differentiated liposarcoma. It typically occurs in older adults and more often occurs in deep locations such as the area at the back of the abdominal cavity, known as the retroperitoneum. 

Fat

The human body is made up of many different types of tissue. Fat is a specialized type of tissue that is found throughout the body. It is made up of large cells called adipocytes that look clear when viewed through a microscope. Fat acts as a storage site for energy and provides warmth for our internal organs.

Types of liposarcoma

There are four major types of liposarcoma:

Well-differentiated liposarcoma and dedifferentiated liposarcoma are closely related tumours. Well-differentiated liposarcoma looks like normal fat. However, unlike normal fat, well-differentiated liposarcoma contains abnormal-looking cells fat cells. Some of these abnormal cells are called lipoblasts.

Some well-differentiated liposarcomas will change over time so that some of the cells no longer resemble normal fat. This process is called dedifferentiation and the cancers that emerge from this process is called dedifferentiated liposarcoma.

In comparison to well-differentiated liposarcoma, dedifferentiated liposarcoma is associated with a worse prognosis. The tumour can come back after your initial surgery (recurrence) and can sometimes spread to other parts of the body. The spread of tumour cells to another part of the body is called metastasis.

How do pathologists make this diagnosis?

The first diagnosis of dedifferentiated liposarcoma 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.

After a pathologist makes a diagnosis of dedifferentiated liposarcoma or suggests the diagnosis as a possibility, the patient is usually treated first with surgery to remove the tumour. Some patients may receive chemotherapy and/or radiation therapy before surgery. When the tumour is surgically removed as a resection specimen, it is sent to pathology for examination.

Histologic grade

Grade is a word pathologists use to describe how different the cancer cells look and behave compared to normal fat cells. The grade can only be determined after a sample of tumour has been examined under the microscope.

Dedifferentiated liposarcomas are given a grade based on an internationally recognized system created by the French Federation of Cancer Centers Sarcoma Group (FNCLCC).  If you have been diagnosed with a dedifferentiated liposarcoma, your pathologist will determine the French Federation of Cancer Centers Sarcoma Group grade of your tumour by looking for three microscopic features:

  • Tumour differentiation – Tumour differentiation describes how closely the cancer cells look like normal cells. Tumours that look very similar to normal cells are given 1 point while those that look very different from normal cells are given 2 or 3 points. Dedifferentiated liposarcomas are usually assigned 3 points.
  • 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.
  • 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.

Your pathologist will give each feature a certain number of points (from 0 to 3) and the total number of points determines the final grade of the tumour.

  • Grade 1 – 2 or 3 points.
  • Grade 2 – 4 or 5 points.
  • Grade 3 – 6 to 8 points.

According to this system, dedifferentiated liposarcomas are typically high-grade tumours and usually receive a grade of 2 or 3.  High-grade tumours are associated with a worse prognosis.

Genetic 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 DNA changes that can be found with special molecular tests.  Dedifferentiated liposarcomas demonstrate amplification of the gene MDM2.  Amplification is a word pathologists use to describe cells that have increased numbers of the same gene or multiple copies of the same gene.

Your pathologist may perform molecular tests on your dedifferentiated liposarcoma to confirm the presence of amplification of the MDM2 gene. 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 tumour has been surgically removed. If your pathologist is certain that your tumour is a dedifferentiated liposarcoma, 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 tumours less than 5 cm are less likely to spread to other parts of the body and are associated with a better prognosis.

Tumour extension​

Most dedifferentiated liposarcomas tend to occur in deep sites such as the back of the abdominal cavity (known as the retroperitoneum). Dedifferentiated liposarcomas can grow into or around organs and blood vessels.

Your pathologist will examine samples of the surrounding organs and tissues under the microscope to look for cancer cells. Any surrounding organs or tissues 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 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.

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

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.

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.

lymphovascular invasion

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.

Margins

A margin is any tissue that was cut by the surgeon to remove the tumour from your body.  Depending on the type of surgery you have had, the margins can include bones, muscles, blood vessels, and nerves that were cut to remove the tumour from your body.

Margin

All margins will be very closely examined under the microscope by your pathologist to determine the margin status. A margin is considered negative when there are no cancer cells at the edge of the cut tissue. A margin is considered positive when there are cancer cells at the 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 (local recurrence).

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.

Lymph node

Many cancers can spread to the lymph nodes, but dedifferentiated liposarcoma 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.

Pathologic stage

​The pathologic stage for dedifferentiated liposarcoma 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 dedifferentiated liposarcoma

The tumour stage for dedifferentiated liposarcoma 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.

Tumour stage for tumours starting in the 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.

Tumour stage for tumours starting on the outside of the 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.

Tumour stage for tumours starting in the 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.

Tumour stage for tumours starting in the space at the very back of the abdominal cavity (retroperitoneum):

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.

Tumour stage for tumours starting in the space around the eye (orbit):

T1 – The tumour is no greater than 2 centimetres in size.
T2 – The tumour is greater than 2 centimetres 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.

If after microscopic examination, no tumour is seen in the resection specimen sent to pathology for examination, it is given the tumour stage pT0 which means there is no evidence of primary tumour.

If your pathologist cannot reliably evaluate the tumour size or the extent of growth, it is given the tumour stage pTX (primary tumour cannot be assessed).  This may happen if the tumour is received as multiple small fragments.

Nodal stage (pN) for dedifferentiated liposarcoma

Dedifferentiated liposarcoma is given a nodal stage between 0 and 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 dedifferentiated liposarcoma

Dedifferentiated liposarcoma 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 June 27, 2021)
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