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What do all these words mean? (Part 1)

What is a neoplasm?

A neoplasm is an abnormal growth of cells. Systemic mastocytosis is a neoplasm because your body makes too many mast cells. Cancers are all neoplasms, but not all neoplasms are cancers. SM is not cancer.


What is a myeloproliferative neoplasm (MPN)?

Myelo- means “related to granulocytes”, cells that store chemicals in granules. Mast cells are a type of granulocyte.

Proliferative means “cell growth”.

So together you have “growth of too many granulocytes”.


What are receptors?

Receptors are proteins on the outside of cells. They have very unique and specific shapes, but it is easier to think of them as being shaped by cups. Only very specific molecules fit into these cups. When the molecule is in the receptor, the cell knows to do something. What this something is varies a lot from receptor to receptor.

For example, when an IgE antibody binds to the IgE receptor on a mast cell, the mast cell degranulates. However, not any molecule would be able to bind in the IgE receptor and cause this action.


What are antibodies?

These are large proteins that help the immune system identify and destroy things like bacteria and viruses. Sometimes your body mistakenly makes antibodies to things inside the body. This causes autoimmune disease.

In labs, antibodies are very useful. There are ways to make antibodies to almost anything in the lab. Using these lab made antibodies, scientists are able to test for specific structures that tell us what cells are present in a sample and how the cells are working.


What are immunoglobulins?

They are the same as antibodies.


What does CD mean? Like in CD117?

CD means “cluster of differentiation”. This means that it is a protein or group of proteins on the surface of a cell that is recognized by an antibody. This means that in a lab, if I use an antibody called “ABC123” and it binds to a specific protein on the outside of cells, that protein will be called “CD-ABC123”.

Over time, as we learn more about “CD-ABC123”, we may realize that this protein is made by a gene called “Wow”. So some people will call it “Wow” and some will continue to call it “CD-ABC123”, which can be confusing. Generally speaking, scientists who work with antibody testing usually use the “CD-ABC123” name and doctors use the “Wow” name. However, both names are still correct.

Receptors are often given “CD” names, but not all “CD” molecules are receptors. Some “CD” molecules are on the outside of cells to do other things, like help cells stick to other cells.


What is CKIT?

CKIT is a receptor that is found on all mast cells, whether or not a person has mast cell disease. The CKIT receptor is also called CD117. They are the same thing. CKIT is sometimes also called KIT. They are also the same thing.

The molecule that fits in the CKIT receptor is called stem cell factor (SCF). When SCF binds the CKIT receptor, it tells the mast cell to stay alive much longer than it is supposed to. It also starts a process that tells mast cells to make more mast cells.


CKIT (CD117) is only found on mast cells?

No, other normal cells have CKIT (CD117) on their surface. Epithelial cells in the skin, breast and some parts of the brain express CD117. Some stem cells in the bone marrow and melanocytes also express CD117. Smooth muscle and fibroblasts do not express CD117. This is important because smooth muscle and fibroblasts are often found close to the cells we might be looking for that may be positive for CD117.

However, when found on cells that don’t normally express CD117, it can be a sign of cancer – but ONLY if these cell types don’t normally have CD117 on their surfaces. Examples of cancers that express CD117 include angiosarcoma and Ewing sarcoma.