Understanding the CD20 Marker in Lymphoma

What is CD20 and How Does it Help in Lymphoma Treatment?

Ross Hutchins receives treatment for Hodgkin's lymphoma. Bryn Lennon / GettyImages

Definition: CD20 Tumor Marker

CD20 is a CD marker - a molecule on the cell surface that can be used to identify and type a particular cell in the body. CD20 is found on the surface of B cells, but lets back up and make this easier to understand.

What are CD Markers?

CD markers are molecules that are found on the surface of cells in our bodies. You may hear them called antigens - and an antigen is basically anything on the surface of a cell that can be recognized by our immune system.

For example, our white blood cells may recognize antigens on the surface of bacteria that enter our bodies and realize that they do not belong.

Every cell in our bodies has a CD marker, and altogether there are more than 250 of these antigens. The term CD stands for cluster of differentiation - and again, is one way in which cells can be told apart.

Being able to identify these becomes important when you cannot otherwise recognize the type of cell.

CD Markers and B Cells and T Cells

Lymphomas are cancers of the type of white blood cell known as lymphocytes. There are two types of lymphocytes - B lymphocytes or B cells, and T lymphocytes or T cells. Both types of lymphocytes help to protect our bodies from infections.

Even though B cells and T cells have different functions, and cancers of each of these kind of cells can act very differently, it can be difficult to tell the difference between the 2 under a microscope.

Kind of like 2 identical twins who behave very differently and respond to people differently but look alike on the outside.

What Exactly is CD20?

CD20 is an antigen that is found on the surface of B cells but not T cells.

An example of where this is important fits with the identical twin analogy above.

There are 2 different cancers that look like identical twins under the microscope, but behave very differently (as far as the course of the disease) and respond differently (not to people but to treatments.) 

Diffuse large B cell lymphoma (DLBCL) is a cancer involving B cells. Under the microscope the cells look just like the cancerous T cells found in anaplastic large cell lymphoma (ALCL). Both of these cancers have large, "cancery" looking cells and can be otherwise indistinguishable.

The difference is that CD20 is on the surface of B  cells, so that a CD20 antigen test would be positive for DLBCL but negative for ALCL.

How is it Tested?

A special technique called immunohistochemistry (IHC) is used to identify CD20 and determine whether an abnormal cancerous white blood cell (lymphocyte in particular) is a B-cell or T-cell.

What Does it Mean for Treatment?

Treatment and prognosis for B-cell and T-cell lymphomas are often different.

A newer category of medications called monoclonal antibodies work very well for some lymphomas.

  Just as our bodies make antibodies to fight off bacteria and viruses, monoclonal antibodies are man made antibodies designed to fight off cancer cells. And just as our bodies make antibodies that recognize antigens on bacteria an viruses, these monoclonal antibodies recognize antigens on the surface of cancer cells; in this case, CD20.

Using a monoclonal antibody that binds to CD20 will therefore only work against a cancer with CD20 antigens on the surface, such as ALCL in the analogy above.

Monoclonal Antibody Treatment and CD20

There are several monoclonal antibodies that are now being used. Monoclonal antibodies that treat B cell lymphomas and leukemias with the CD20 antigen on the surface of the cells include:

  • Rituxan (rituximab)
  • Zevalin (ibritumomab tiuxetan)
  • Bexxar (tositumomab)
  • Gazyva (obinutuzumab)
  • Arzerra (ofatumumab)

Coping with Lymphoma

As you've reached this page, you are taking a great step forward in being an active participant in your care. Studies have found that learning as much about your disease as possible, and playing an active role in your care, helps not only cope with the anxiety of cancer, but may help with outcomes as well.  Reach out to family and friends. Cancer can literally take a village, and don't be afraid to ask for help.  Check into the wonderful online community of people with leukemia and lymphoma - people you can access 24/7 for support and with questions. And make sure you are your own advocate in your cancer care. Medicine is changing and oncologists not only tolerate but expect to work side by side with you to tailor a treatment program that is best for you as a person.


National Cancer Institute. Adult Non-Hodgkin Lymphoma Treatment – Health Professional Version (PDQ). Updated 01/15/16. http://www.cancer.gov/types/lymphoma/hp/adult-nhl-treatment-pdq

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