Well differentiated liposarcoma

This article was last reviewed and updated on November 19, 2019.
by Bibianna Purgina, MD FRCPC

Quick facts:

  • Well differentiated liposarcoma is a cancer made up of fat.

  • It can start anywhere in the body but the most common location is the abdomen.

  • This tumour affects adults and rarely happens in children.

 

Normal fat

The human body is made up of many different types of tissue. Fat is a special type of tissue that is found throughout the body. Fat is made up of large cells called adipocytes that look clear when viewed through a microscope.

What is well differentiated liposarcoma?

Well differentiated liposarcoma is a cancer made up of fat. Well differentiated liposarcoma can start anywhere in the body but the most common location for this tumour is the abdomen.

 

Unlike normal fat, well-differentiated liposarcoma contains abnormal (atypical) 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 these cancers are then called dedifferentiated liposarcoma.

 

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

The first diagnosis of a lipoma may be made after a small sample of tissue is removed in a procedure called a biopsy. Surgery can then be performed to remove the entire tumour.

Tumour size

This is the size of the tumour measured in centimeters. Tumour size will only be described in your report after the entire tumour has been removed. The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.

Grade (French Federation of Cancer Centers Sarcoma Group/FNCLCC)

Grade is a word pathologists use to describe how different the cancer cells look and behave compared to normal fat cells (adipocytes). Well differentiated liposarcoma is given a 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.

 

How do pathologists determine the tumour grade?

Your pathologist will determine the French Federation of Cancer Centers Sarcoma Group grade after examining the tumour under the microscope. The grade is based on three features which are described below. Points are given to each feature (from 0 to 3) and the total number of points determines the final grade of the tumour.

 

  1. Tumour differentiation – Tumour differentiation describes how closely the cancer cells look like normal, healthy fat cells. Tumours that look very similar to normal fat cells are given are given 1 point while those that look very different from normal fat cells are given 2 or 3 points.

  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. Necrosis - Necrosis 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.

 

The final grade is based on the total number of points given to the tumour:

  • Grade 1 – 2 or 3 points.

  • Grade 2 – 4 or 5 points.

  • Grade 3 – 6 to 8 points.

Why is this important? High grade tumours (grade 3) look and behave the least like normal cells and are associated with worse prognosis. High grade tumours are more likely to re-grow after treatment or to spread to another part of the body.

Necrosis

Necrosis is a type of cell death. Necrosis is commonly seen in cancers. Your pathologist will closely examine the tumour for evidence of necrosis.

Why is this important? Necrosis increases the tumour grade (see Grade above) and is associated with worse prognosis.

Perineural invasion

Nerves are like long wires made up of groups of cells called neurons. Nerves send information (such as temperature, pressure, and pain) between your brain and your body. Perineural invasion means that cancer cells were seen attached to a nerve.

Why is this important? Cancer cells that have attached to a nerve can use the nerve to travel into tissue outside of the original tumour. This increases the risk that the tumour will come back in the same area of the body (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.

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.

Why is this important? Lymphovascular invasion 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 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 cancer 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 cancer cells are to the edge of the cut tissue. Margins will only be described in your report after the entire tumour has been removed.

A margin is considered positive when there are cancer cells at the very edge of the cut tissue.

 

A negative margin means there were no cancer cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest cancer cells were to a margin. The distance is usually described in millimeters.

Why is this important? A positive margin is associated with a higher risk that the tumour will grow back (recur) in the same site after treatment.

Treatment effect

​If you received treatment (either chemotherapy or radiation therapy) for your cancer prior to the tumour being removed, your pathologist will examine all of the tissue submitted to see how much of the tumour is still alive (viable).

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 a metastasis

 

Your pathologist will carefully examine each lymph node for cancer cells. Lymph nodes that contain cancer cells are often called positive while those that do not contain any cancer cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain cancer cells.

Why is this important? Well differentiated liposarcoma rarely spreads to lymph nodes. However, if cancer cells are found in a lymph node this increases the risk that the cancer will spread to other parts of the body.

Pathologic stage

​The pathologic stage for well differentiated 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 worse prognosis.

 

Pathologic stage is not reported on a biopsy specimen. It is only reported when the entire tumour has been removed in an excision or resection specimen.

Tumour stage (pT) for well differentiated liposarcoma

The tumour stage for well differentiated liposarcoma varies based on the body part involved. For example, a 5 centimeter tumour that starts in the neck 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 centimeters in size.

  • T2 – The tumour is between 2 and 4 centimeters in size.

  • T3 – The tumour is greater than 4 centimeters 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 centimeters in size.

  • T2 – The tumour is between 5 and 10 centimeters in size.

  • T3 – The tumour is between 10 and 15 centimeters in size.

  • T4 – The tumour is greater than 15 centimeters 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 centimeters in size.

  • T2 – The tumour is between 5 and 10 centimeters in size.

  • T3 – The tumour is between 10 and 15 centimeters in size.

  • T4 – The tumour is greater than 15 centimeters in size.

 

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

  • T1 – The tumour is no greater than 2 centimeters 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 well differentiated liposarcoma

Well differentiated liposarcoma is given a nodal stage of 0 or 1 based on the presence of cancer cells in a lymph node. If no cancer cells are seen in any of the lymph nodes examined, the nodal stage is N0. If cancer cells are seen in any of the lymph nodes examined, the nodal stage becomes N1.


Metastatic stage (pM) for well differentiated liposarcoma 

Well differentiated 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.

MDM2

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.

MDM2 is a gene that promotes cell division (the creation of new cells). Normal cells and those in non-cancerous (benign) tumours have two copies of the MDM2 gene. In contrast, well differentiated liposarcomas have more than two copies of the MDM2 gene. 


A test called florescence in situ hybridization (FISH) is commonly used to count the number of MDM2 genes in a cell. 

 

Why is this important? An increased number of genes (more than two) is called amplification and supports the diagnosis of well differentiated liposarcoma.

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