NCCN Guidelines for Patients™: Multiple Myeloma
1.3 What are M-proteins?
As shown in Figure 4, normal antibodies are made of
two heavy protein chains and two light protein chains.
Heavy chains are one of five forms (A, D, G, E, or M),
and light chains are one of two forms (kappa or lambda).
The form of heavy chain present defines the class of
antibody. Most people with myeloma—about 60 out of
every 100—have myeloma cells that make G antibodies.
Figure 4. Antibodies made by a plasma cell versus
a myeloma cell
Illustration Copyright © 2012 Nucleus Medical Media, All rights reserved.
The antibodies made by myeloma cells aren’t normal.
They are called monoclonal proteins or M-proteins
because they are an excess of one class of antibody.
M-proteins are made uncontrollably and not in
response to a specific germ in the body. They don’t
help to fight infections.
In most patients, myeloma cells make very large
amounts of M-proteins. The most common M-protein
is the IgG kappa subtype (i.e. G heavy chain and
kappa light chain). Rarely, people with myeloma have
few or no M-proteins. This is called oligosecretory or
As shown in Figure 4, myeloma cells also tend to make
more light chains than needed to form a complete
M-protein. These are called free light chains because
they aren’t attached to a heavy chain as in a normal
antibody. High levels of free light chains are found
in the urine of most people with myeloma (75 out of
every 100 people). In about 20 out of 100 people
with myeloma, the myeloma cells only make free light
chains and no complete M-proteins. Doctors call this
light chain myeloma or Bence Jones myeloma.