Tag Archives: psma

PSMA PET-CT scans for Prostate Cancer


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PSMA stands for Prostate Specific Membrane Antigen, which is a protein (enzyme) that is expressed on the surface of prostate cancer cells (and on a few other cell types). As with many cell surface proteins, you can find ligands that will bind to the protein, and then label these with radioactive isotopes that allow imaging. PET stands for Positron Emission Tomography, and of course, CT stands for Computerized Tomography. When you put these technologies together, you obtain a powerful way to look for prostate cancer that has spread outside the prostate gland. The physics of this (how a positron interacts with an electron, releasing gamma photons at 180 degrees) is very cool, but probably of interest only to the most nerdy. (I made a cloud chamber for my 7th grade science project and my hiking buddy is a nuclear medicine doc who wrote a definitive text on the math/science of his craft…so go figure).

Prior to developing PET agents for prostate cancer, we had standard CT scans and bone scans and we used these to determine whether someone with, for example, a very high PSA or high Gleason score had cancer deposits that had escaped (metastasized) from the prostate. If so, it was felt that putting them through surgery or radiation treatments in an attempt to cure was fruitless and exposed the patient to the unnecessary toxicity risks (impotence, incontinence, rectal damage, etc.) Especially if they had symptoms (e.g. bone pain), hormone treatment reducing testosterone was the best approach. If you had a rising PSA several years after local treatment, the question was always, “Where is the cancer?” but the sensitivity of routine bone and CT scans was quite limited not showing anything until the PSA reached 10 or so at which time ~1/2 of scans would be positive. Screen Shot 2020-04-26 at 7.26.14 AMThis figure illustrates the difference in sensitivity. A normal sized lymph node on CT scan (left) is revealed to  contain prostate cancer with the PET isotope technique (right). At present, the only approved PET scan in the U.S. is fluciclovine, the “Axumin” scan, which the FDA approved for detecting cancer in patients with rising PSA, but not in newly diagnosed patients. In several studies PSMA-PET CT scans are even more sensitive (about 3x) than Axumin. At the risk of calling up an overused phrase, “this changes everything”.

First, it is clear that many high risk patients we would previously have treated with surgery or radiation to the prostate hoping to cure them might now be found to have prostate cancer deposits outside of the treatment target (prostate or prostate + pelvic lymph nodes). A superb study in this month’s Lancet found that PSMA PET-CT scans provided higher sensitivity (85% vs 38%) and specificity (98% vs 91%) than routine bone and CT scans in high risk patients (PSA >20, Gleason 4+3 or worse). Does this mean we shouldn’t treat the prostate in high risk patients with positive scans? In the study, conventional imaging changed the management in 15% of men, while PSMA PET-CT imaging changed the plans in 28% (p=0.008). Should all high risk patients have a PSMA PET-CT before deciding on treatment? Should the FDA approve this scan quickly? (It is currently available only in research centers and not covered by insurance…read my blog on how to search for such studies or click here).

Second, what about treating a small number of prostate metastases (oligometastatic prostate cancer) in a patient who was treated years ago and now has a rising PSA? Ongoing investigations suggest this might delay the need for hormone therapy in such patients or potentially even cure some of them. But the PSMA PET-CT isn’t perfect. How high do you let the PSA go up before ordering such a scan? – the farther it rises, the more likely the scan will show something, but that gives the cancer more time to spread. A negative scan is no guarantee there aren’t many more foci of a few prostate cancer cells that will eventually show up elsewhere in the body. Is this some version of Whack-a-mole? And how do we define “cure” anyway?? (My personal definition is that you die from something else, regardless of your PSA or scan results).

Finally, since even at research centers the PSMA PET-CT scan may cost you $3,000 or so, is it worth it? It is “free” in the European health care systems, but we all know nothing is free – even if Medicare pays for something it costs society and ultimately must be accounted for in terms of value. Medicare covered PSMA PET-CT’s vs fixing pot holes and bridges? How about finding a treatment for SARS Co-V2 instead? No easy answers, but if you are like me, homebound as a “high risk” senior citizen, plenty to think about. Wash your hands, wear your mask, and enjoy your grandkids on Zoom!

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Filed under General Prostate Cancer Issues, Oligometastatic prostate cancer, Prostate cancer therapy, Targeted treatment

New findings from clinical trials 2020


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There are a number of ongoing trials or completed trials that represent attempts to develop new approaches to prostate cancer. I am sometimes asked what I know or think about them (often not as much as I would like) from various investment consultants, so I thought rather than respond to a recent list, I would just use it to explain the trials for readers of this blog. Perhaps when your friends ask you whether there is “anything new out there”, you can point them to some of these.

The PROFOUND, TALAPRO-1, TRITON-2 studies are all designed to evaluate the efficacy of small molecule drugs that inhibit “PARP” which stands for an enzyme (Poly ADP-ribose polymerase) that is involved in DNA repair. It turns out that patients who inherit a damaged/mutated version of any of several enzymes that help cells maintain their DNA integrity (BRCA1/2 being an example you may have heard of – when mutated it leads to the development of breast and ovarian cancers as well) are more likely to get prostate cancer, and often it is of the more aggressive variety. It is also a frequent condition of prostate cancer metastases in patients who no longer respond to hormone therapies (leuprolide, abiraterone, enzalutamide, etc). These patients appear to be uniquely sensitive to PARP inhibitors and several pharmaceutical companies are developing them. Olaparib and rucaparib received breakthrough designation from the FDA for accelerated development. In the PROfound trial, patients who had progressed on either enzalutamide (Xtandi) or abiraterone (Zytiga) were randomized to receive the “other” new hormonal agent or the PARP targeted drug olaparib (Lynparza). As reported by my friend/colleague Maha Hussain, the olaparib treated patients fared significantly better than the patients who received the “other hormone”. The take-home message from these trials is that we now have ways to look at the molecular underpinnings of resistant prostate cancer. If you have metastatic prostate cancer, ask your physician about the genomic tests that can be done to see if you might benefit from one of these new drugs.

In a somewhat similar design, the CARD trial evaluated treating patients who had had been treated with docetaxel (Taxotere) and then progressed while on enzalutamide or abiraterone with cabazitaxel (Jevtana) rather than the alternate hormone targeted drug. Chemotherapy with cabazitaxel was the better approach. This was similar to a previous trial called FIRSTANA that looked at alternatives of mitoxantrone or cabazitaxel in progressing docetaxel treated patients. The take-home message here is that chemotherapy with cabazitaxel may be a good choice if you don’t fit the PARP profile above, and studies have shown that cabazitaxel is preferred in terms of side effects compared to docetaxel.

Finally, I will comment on the VISION trial. PSMA stands for prostate specific membrane antigen and it is expressed on prostate cancer cells. It can be used to direct pet-scanning agents to metastatic cancer deposits and these scans are currently the most sensitive ones we have for detecting prostate cancer. These scans are available at several centers in the U.S. and are now routinely used in Europe. By linking a more radioactive isotope, Lu177 to the PSMA, you can also treat prostate cancer and early results in patients with progressive hormone refractory disease have been encouraging with more than half of patients responding. The VISION trial compares this approach with cabazitaxel to see which might be the best, but in the long run, it may be possible to use both agents, and potentially to use them even earlier before resistant disease has developed.

We have entered an era when there are numerous promising options for treatment, and the key is to get as many men  as possible to participate so we can finish the trials and get these new agents approved. We also have drugs like cabazitaxel that have been approved for some time and a better idea of when to use them. Working with a team that has the expertise to guide a patient and offer the right choices at the right time is essential for the best outcomes.

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Filed under Prostate cancer therapy, Targeted treatment