Video: Body Scans for Prostate Cancer
THE STAGING GUIDE VIDEO SERIES | TRANSCRIPTION:
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 determination is with a body scan. Classically, this has consisted either of a bone scan, a CT scan, or an MRI, or even all of the above. Bone scans, as you can imagine, are good for looking at the bones. CT 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 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 bones 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 to finding small lymph node metastases. However, they've been standard for many years, and classically, when people have PSAs over 10, a 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 3Tesla multi parametric MRI. Standard body MRIs, open MRIs, are perfectly fine at looking at lymph nodes. It's a 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 who have known metastatic disease - to track the progression or regression of 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 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 metastasis 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 CT scan alone or an MRI can accomplish.
It's 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 1. 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 CT scans and MRIs that, for relapsed disease, there's not a practical reason to be using CT scans or MRIs any further in this world. The question also arises, "Why don't we use Axumin PET scans for 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 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 C-11 Acetate PET scans, C-11 Choline PET scans, PSMA-Gallium PET scans, and F-18 PET scans. The technology being produced with these new types of PET 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 cost.
Always remember when looking at a scan report, that these are simply images of spots and shadows in the patients 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 in 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 do 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 cells 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 was 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 oligometastases. Patients can sometimes still be cured with oligometastases. These scans that we are 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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