>>>DR.
JAY HARNESS: PET scans and particularly PET scans used with a CT scan is a very helpful
diagnostic tool and the effort to try and stage a patient who we know is lymph node
positive.
So typically, as part of the initial evaluation process, if we have done a biopsy of the lymph
nodes and know the lymph nodes are involved, and then almost all of us will order a PET-CT
scan of the chest, abdomen, and pelvis is a way of initial staging and looking to see
if the cancer has gone elsewhere.
Many medical oncologists then follow their patients periodically, who are lymph node
positive or who had locally advanced breast cancers with periodic PET-CT examinations
again looking for distant failure or distant recurrence of cancer, time period six months
a year, several years down the road after the initial treatment.
One of the questions I have been asked is about the ability of a PET scan to detect
metastasis in lymph nodes, particularly at the micro level, tiny little metastasis within
lymph nodes.
With all technologies, there are limits to what we can do with technologies, and in imaging
technologies typically we are talking about limits of what is called resolution.
In other words, how finite can we get in our ability to see small areas of abnormalities.
Most CT and PET scans are certainly down in 3 mm or so range of detection ability; also
with a PET scan the sort of counts that we get and the intensity of the uptake and how
it is registered on the equipment is a reflection of burden of a disease.
As PET scans are currently put together and with the current resolution, I do not believe
that PET scans can detect micrometastasis in lymph nodes.
The way we typically detect micrometastasis in lymph nodes are with sentinel lymph node
biopsies which I have previously described the importance of that approach and staging
here at Breast Cancer Answers or in the process (how do I put this) in the process of dissecting
and looking at all the lymph node tissue that we have taken out either with a lymph node
dissection or a sentinel lymph node biopsy.
When we make fine little sections in the lymph node then often we can see micrometastasis.
So I think what is the bottom line here, please remember that all technologies that we have,
have limitations to what they can do.
I am unaware of the ability of PET scans to detect micrometastasis in lymph nodes; however,
it is an important technology and I have tried to give you the overview of how that technology
is currently utilized.
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