Hi, I'm Dr. Scholz. Let's talk about prostate cancer.
Today we're going to talk about body scans for staging and monitoring prostate cancer.
One of the most important things when treating any kind of cancer, including prostate cancer,
is whether or not the disease has metastasized. The most reliable and accurate way to make
that determinization is with a body scan. Classically, this has consisted of either
a bone scan, a CAT scan, or an MRI, or even all of the above. Bone scans, as you can imagine,
are good for looking at the bones. CAT scans and MRIs are better at looking at soft tissues.
So let's talk about the classical bone scan first, called a nuclear medicine study or
a technetium-99. These scans involve going to a special facility, getting an injection,
the substance percolates around the body, and lights up spots in the bone that could
be cancerous. Other things can light up as well such as arthritis, and so expert reading
is essential. Typically, bone scans are not going to show any type of prostate cancer
unless the PSA is above 10, 20, 40, or 50 so doing bone scans when the PSA is under
10 is usually a waste of time and even risks false positives.
Body scans, CT scans and MRIs looking for enlarged lymph nodes, particularly in the
pelvis or the abdomen, are useful only if the cancer has expanded to over a half-inch
in size. So it's, of course, useful to know that information, but these scans are not
particularly sensitive for finding small lymph node metastases; however, they've been standard
for many years and classically when people have PSAs over 10 as bone scan will be performed
and also a body scan, either a CT scan or an MRI.
Let me make it clear that when we're talking about MRI in this role, looking at lymph nodes,
this is not the same thing as trying to look inside the prostate with a Three Tesla Multi-Parametric
MRI. Standard body MRIs, open MRIs are perfectly fine at looking at lymph nodes. It's different
technology and different training. Although they're both called MRI, they're not the same
thing.
Bone scans and body scans are used in men who are newly diagnosed that have PSA levels
over 10. They're used in advanced disease, men that have known metastatic disease, to
track the progression or regression of the disease as a result of treatment. Spots that
are enlarging show cancer is progressing, the treatment is not working. Spots that are
shrinking show effective therapy and indicate that therapy can be continued.
New technology is revolutionizing the way we find cancer that's spread. In particular,
I'm talking about PET scans—positron emission tomography. PET scans are much more sensitive
and accurate for finding small metastases than the traditional MRI or CT scan. There
are actually four different types of PET scans. Three are in development and one is FDA approved
already. The one that's FDA approved is called Axumin and this is a radioactive substance
injected into the bloodstream, and it will help delineate abnormal cancerous lymph nodes
rather accurately—far better than anything a CAt scan alone or an MRI can accomplish.
This is very important for men that have had previous surgery or radiation and now have
developed a rising PSA. Historically, lymph node metastases could only be seen if the
PSA was 10, 20, or 30. Now with new Axumin PET scans, we can detect cancer with PSAs
as low as one. This changes the whole complexion of how we manage prostate cancer and provides
very useful information to guide therapy. Axumin PET scans are so superior to CAT scans
and MRIs that for relapsed disease there's not a practical reason to be using CAT scans
any further in this role.
The question also arises, why don't we use Axumin PET scans in men that are newly diagnosed?
If it's a better tool, why not? Basically, at this point, clinical studies proving its
effectiveness don't exist and it's very difficult to get insurance coverage. There are considerations,
logical considerations, however, to think about using one of these PET scans in people
who are looking for metastatic disease that have been recently diagnosed, but so far this
is not FDA approved.
There are a number of new investigational PET scans that will probably be on the market
within a couple of years. Some of these scans are available for off-label use although insurance
typically won't cover them. The type of scans I'm talking about are c11 Acetate PET scans,
C11 Choline PET scans, PSMA-Gallium PET scans, and F-18 PET scans. The technology being produced
with these new types of scans is truly remarkable and the technology is so good it's almost
certain that at some point FDA approval will occur. Perhaps two or three years from now.
In the meantime, for patients who are looking for the most precise information searching
online for centers of excellence that are doing these new types of scans may be useful
and may be worthwhile even if you have to pay the out-of-pocket costs.
Always remember when looking at a scan report that these are simply images of spots and
shadows in the patient's body. There is no proof that any of those spots are cancerous.
There are patterns that experts can interpret that are likely to be cancer or highly probably
to be cancer, but I've seen some terrible mistakes made by people over-interpreting
information on a scan as being gospel truth. Abnormalities can be double-checked with biopsies
or perhaps another type of scan. An abnormality on a bone scan can be cross-checked with an
MRI of the bone to confirm that the abnormality being seen is truly cancerous.
When using body scans to monitor advanced prostate cancer, people often inquire, "how
frequently do the scans need to be repeated?" There's no precise answer, but you can think
of the range of as frequently as every three months and as infrequently as once a year.
The answer depends on how dynamic the situation is. If the PSAs are changing quickly you're
going to do scans more quickly; if things are indolent and languid and not changing
quickly, a scan once a year may be sufficient.
How to PET scans actually work? Well, it depends on the type of PET scan. For example, Axumin
PET scans use radioactive amino acids that are absorbed into the cancer cells. Cancer
cells that are growing absorb amino acids actively and this is how the cancer cells
light up when they're looked at under a scanner. C-11 Acetate and C-11 Choline use radioactive
fat substances. Fast-growing cancer cells use energy and fat is high-energy. PSMA/PET
scans are identifying a unique molecule on the surface of the cancer cell called prostate-specific
membrane antigen (PSMA) and a ligand clips onto the surface of the cancer cell and thus
detects its presence or absence. F-18 PET bone scans actually detect increased bone
turnover near the cancer cells because cancer cells in the bone irritate the bone matrix
causing increased metabolism.
New scanning technology has changed the way we manage prostate cancer more than any other
recent development. doctors are detecting cancer at much earlier stages. Historically,
metastatic disease has been thought to be incurable. This is partly because older scans
were detecting metastatic disease at very advanced stages. Now, with newer technology,
just one or two small metastases are being detected. This is called oligometastasis.
Patients can sometimes still be cured with oligometastases. These scans that we're talking
about, particularly PET scans, are revolutionizing the way that we manage prostate cancer. It's
important that you get up-to-date information about how to utilize these scans to their
greatest benefit.
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