PSMA Imaging: What It Is and How It’s a Game-Changer

In the first video in GU Oncology Now’s Round the Wire series on PSMA Imaging, moderator Dr. Neeraj Agarwal and Dr. Jeremie Calais review the basics of PSMA as a biological target for PET imaging of prostate cancer. Dr. Calais continues the discussion covering how PSMA imaging is different from other available PET scans and what makes PSMA imaging a game-changer.

 

Dr. Agarwal:

Hi, my name is Dr. Neeraj Agarwal. I’m a GU Medical Oncologist and a Professor of Medicine at the Huntsman Cancer Institute, University of Utah, Salt Lake City. Today, we are going to discuss the role of PSMA imaging, how it is used in the treatment of prostate cancer, and after that, we’ll discuss the role of precision oncology as far as management of prostate cancer is concerned. With me, we have Dr. Jonathan Tward, Dr. Scott Tagawa, and Dr. Jeremie Calais. I would ask Dr. Tward to introduce himself first.

Dr. Tward:

Thank you so much, Dr. Agarwal. It’s a pleasure to be on this esteem panel. My name is Jonathan Tward; I’m a radiation oncologist. I specialize in treating GU Cancers, and I work at the Huntsman Cancers Institute at the University of Utah.

Dr. Agarwal:

Dr. Tagawa.

Dr. Tagawa:

I’m also happy to be here. My name is Scott Tagawa. I’m a GU medical oncologist at Weill Cornell medicine, New York Presbyterian Hospital in New York.

Dr. Agarwal:

Dr. Calais.

Dr. Calais:

Hello everyone. Thank you very much for inviting me. It’s a pleasure for me to be here. I’m a nuclear medicine physician, and I lead the Theranostics Program at UCLA, and it’s my great pleasure and a honor to share my experience with PSMA PET approach.

Dr. Agarwal:

Thank you very much for being here. So let’s start the discussion today about the role of PSMA imaging. We have been hearing about PSMA imaging for many years, but this has literally come to the forefront with the success of the VISION Phase III trial.  Sites, hospital and practices across the country are gearing up for using PSMA imaging in the diagnosis and management of prostate cancer. So, I’d like to start with Dr. Calais first. What is PSMA imaging? How is it different from other PET scans we have right now in the clinic?

Dr. Calais:

Yes, it’s a very good point. PSMA PET CT imaging is, as it indicates a PET CT imaging technique, just to be sure we’re all on the same page, you have multiple way and multiple biological target for prostate cancer imaging using PET agents. You can do Fluciclovine PET, you can do FDG PET, you can do choline PET. These are metabolic pathway, and it is a different biological target you use to do prostate cancer imaging. Here, we’re looking at overexpression of a cell surface protein called PSMA that is very highly overexpressed by the prostate cancer cells in a great order of magnitude up to 100 on 1000 times, compared to normal tissues on the surrounding. And so these great overexpressions, pretty specific to prostate cancer makes it a very relevant biological target for PET imaging of prostate cancer.

So that’s the first thing. That’s what it does. You go to this target, the protein targets, and then you get some signal out of it that you capture with PET CT scanner, and then you make the image on the whole body level of the biodistribution of the overexpression of this protein. Why it is a game changer compared to any other imaging modalities so far is that this overexpression is so high that it provides very high contrast images with very high tumor-to-background ratio. When you see a map on the scan, it is black on white lesions that you see. Therefore, the scans are pretty easy to read, the lesions are easy to detect and characterize. That’s the game changer much more than with prior other PET imaging agents targeting the metabolic pathway.

Dr. Agarwal:

So, that’s great to hear Dr. Calais. So for our colleagues and community oncologists or urologists or radiation oncologists who have not used PSMA imaging ever in the past or who may not know about PSMA imaging until now, how much more sensitive PSMA imaging is compared to traditional PET scans or bone or CT scans or even fluciclovine PET scan, which has been used in the United States over the last many years?

Dr. Calais:

So, I think PSMA PET CT, most of the data now has arisen during the past five years from 2015 until now. And you had multiple studies comparing head-to-head multiple other imaging techniques to PSMA PETs in various different settings at initial staging, at biochemical recurrence or maybe at more advanced stage of disease. It’s like with progress, the more you go, the more sensitive and specific techniques you get. So, it doesn’t mean we are in the perfect spot now. PSMA PET CT has still some limitations, but compared to any other imaging modality, coming from CT bone scan, then MRI, then choline PET, then fluciclovine PETs, you go more and more sensitive and more and more performing for diagnostic care performances, and now PSMA PETs. That’s the last one.

Maybe in the future, there will be another target, another imaging technique that will be better. But as of now, I describe here chronologic order of this imaging modality techniques for imaging prostate cancer and PSMA PETs outperform all these one, especially at primary staging and at biochemical recurrence. It also has great performances in the advanced setting, but in the advanced setting, all the other imaging already work pretty well because the disease burden is very, let’s say considerable and high. So, there is no real pitfall to be missed here.