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Understanding CD markers

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Updated September 24, 2008

What does CD stand for?

CD stands for Cluster of Differentiation.

Understanding CD markers:

CD markers are a group of special molecules on the surface of the cells in our body. There are more than 250 types of CD molecules. All cells in our body have one or more of them, but they are most useful for classifying WBCs (white blood cells), a type of cell in the blood that protects us from infections.

Why are they important in cancer diagnosis?

There are different types of WBCs and they don’t always look different. The most precise way to identify the different types is to see what CD molecules appear on their surface. This is especially important for diagnosis of blood cancers. Lymphomas and leukemias are cancers of WBCs. To find out the type of WBC affected and the exact type of leukemia and lymphoma, we need to identify the types of CD molecules that the cancer cells have.

As an example, two lymphomas diffuse large B-cell lymphoma (DLBCL) and anaplastic large cell lymphoma (ALCL) often look similar under the microscope with large cancer cells. Yet, their prognosis and treatments are different. CD markers can tell them apart. DLBCL is CD20 positive, while ALCL is CD20 negative but positive for CD30. Pathologists often use CD markers to distinguish between different lymphomas.

Identification of CD molecules:

The molecules themselves cannot be seen with the eye. They are identified using ‘antibodies’ –- matching molecules that will bind to the specific type of CD molecule and also show up under the microscope. Using antibodies in the lab, samples from blood and lymph nodes can be checked for CD molecules and the type of cancer precisely determined.

CD molecules also important for cancer treatment:

Now, we have even better uses for CD molecules. Special drugs have been designed that identify and attack cells that have a particular type of CD molecule. These drugs are called monoclonal antibodies and they can attack only the type of cell that contains the specific target CD molecule. Monoclonal antibodies can also be tagged to drugs or radiation-emitting substances that add to the ability to kill cells that have the specific CD marker on their surface.

Some examples of CD markers targeted in lymphoma treatment:

  • Rituxan (Rituximab) - a monoclonal antibody against CD20.
  • Zevalin (Ibritumomab Tiuxetan) - another antibody against CD20, tagged with a radiation emitting substance (Y90).
  • Bexxar (Tositumomab) - similar to Zevalin, only the radiation emitting substance is different (I131)

Source:

Wintrobe's Clinical Hematology (11th Edition). Editors J.P. Greer, J. Foerster, J.N. Lukens. Published by Lippincott Williams & Wilkins.

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