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Can Darzalex (daratumumab) therapy interfere with response assessment?

Can Darzalex (daratumumab) therapy interfere with response assessment?


This week’s Ask Dr. Durie comes from a patient
taking Darzalex therapy. Otherwise known as daratumumab, a monoclonal
antibody against CD38, or dara for short. The question is: Can the dara, monoclonal
antibody, actually interfere with the response assessment? If there has been a complete remission, can
there be confusion that a small spike is present, that is actually the dara and not the myeloma? The answer to this is yes, there can indeed
be a small spike in the serum that is coming from the dara. This tends to be a very, very small spike
at a level of 0.1 to 0.2 gram per deciliter. So a very, very tiny spike. If the pathologist looks at the serum protein
electrophoresis, the pathologist in the lab can almost always tell that this is a small
spike which is not in the same place as the original myeloma monoclonal spike. And so with some careful review, it can always
be distinguished. The myeloma spike from the patient can be
distinguished from the IgG kappa monoclonal antibody which is, in fact, the Darzalex. The good news is that this would be a confusion
after there has in fact been an excellent response where you are looking to see if there
is a tiny, tiny amount of the myeloma left. Another thing to be aware of, is that, in
this circumstance, there can occasionally be an extra spike, which is called an oligoclonal
spike. And this is a tiny spike that means that the
normal immune system is recovering, and it’s creating small amounts of monoclonal protein
as the recovery process is occurring. So the BOTTOM LINE, in this case, is there
can be a tiny spike which can cause some confusion, but careful review in the lab can normally
detect the dara and be known it is not myeloma. If there really, really is a question, a sample
can be sent off for special testing – testing that has been organized by the Janssen company,
which manufactures the Darzalex – to rule the possibility out that the spike is coming
from dara and is what is causing the confusion. Something very important to be aware of, but
something that can be normally sorted out with careful review of the serum protein electrophoresis
and the immunofixation testing.

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