Using PSMA-PET to Better Understand Recurrence Risk and Inform Therapy Plans: Part 2

By Akhil Abraham Saji, MD - Last Updated: August 15, 2022

An interview with Ida Sonni, MD, a nuclear medicine physician trained in Italy at the University of Rome Sapienza, currently an academic researcher in the department of radiological sciences, integrated diagnostics (IDx), at UCLA.

Interviewed by Akhil Saji, MD, chief urology resident at New York Medical College/Westchester Medical Center.

This is the second part of a 2-part conversation with Dr. Sonni. Watch part 1 here.

Dr. Akhil Saji: Very interesting. Do you know how as clinicians, we can utilize PSMA imaging to predict future biochemical recurrence risk? Is that something that’s being thought about?

Dr. Ida Sonni: Yeah. This is a very relevant question, I believe, from a clinical standpoint. There is not much published that I know of for the use of PSMA PET in the prediction of risk of biochemical recurrence. It is a very important topic, especially from a clinical standpoint, as I was mentioning. The proof of that is that European Association of Urology, they developed these risk scores that divide patients that have BCR or biochemical recurrence of disease after radical treatment into two main groups, based on some clinical parameters.

There’s a group that has higher likelihood of developing the metastases and disease progression, and those that have lower risk. This is based on clinical parameters, as I was saying, like the PSA doubling time, the Gleason score, and the time interval between the therapy and the development of BCR. Obviously, PSMA PET can play a role in this. After primary curative treatment, be it radiation therapy, or radical prostatectomy, almost up to 50% of patients will experience BCR.

What we really want to know is what we want to understand, which one of these patients that experience BCR will develop metastases and disease progression? There are a couple of studies that I can think of. One is a multi-center study that was done between some centers in the United States, UCLA, UCSF Michigan, and in Europe, Germany, and Italy. They looked specifically at PSMA PET used in patients that were stratified based on the EAU’s risk stratification.

They realized that, basically, the PSMA PET is highly associated with the stratification done based on the clinical parameters. The majority of patients that have high risk based on these clinical criteria, so the EAU risk certification criteria, have higher likelihood of having a positive PSMA PET scan. Those that have low risk, they have high likelihood of having a negative PSMA PET scan, but there are also the cases that are discordant.

Those cases in between that have low risk in metastases on PET, or high risk clinically and no metastases on PET, those are the cases that we’re really curious about. I’m curious to look at the long term follow up in these patients, and I’m sure that there will be studies. I know of one study that was published in Australia by Reese Emmitt’s Group. They also looked at patients they were stratified based on the risk certification groups, and also based on the results of PET. They had patients with a positive and a negative PET, patients with a high risk, and patients with a low risk.

Basically, what they were able to show was that both PSMA PET status and the risk groups were independently predictive of event-free survival. They were both predictive independently. This is really important. Absolutely, this is a very relevant question. I believe that PSMA PET has additional prognostic value, and we should be considering adding it in the future of risk management.

Dr. Saji: Okay. Okay. Very interesting. Aside from those specific studies, are there any future clinical trials or currently recruiting trials that you think you’re specifically interested in, or might change our management of certain patient populations?

Dr. Sonni: Yeah, sure. We’ve talked about oligometastatic disease. We talked about radiation therapy planning. I’m really looking forward to seeing the results of a study that we’re conducting at UCLA with UCSF. It’s a phase three randomized study that is looking at patients with biochemical recurrence. These patients were randomized into two groups. One group would receive PSMA PET and salvage radiation therapy based on the results of the PET. The other group would receive conventional imaging and radiation therapy based on the results of the conventional imaging.

This study was done with, basically, the end point of looking at success rate at five years. We’re only looking at patients who will actually receive radiation therapy. This is going to be at five years. I know that the last patient was recruited in 2020. We’re looking forward to the results of this. This is a long term follow up that will prove eventually. As we were mentioning before, that there is actually an impact of these imaging scans on progression for survival.

Overall, it’s a very exciting time for PSMA imaging. I’m looking forward to seeing many more collaborations. I was really happy to see that there were really productive collaborations in the studies that were involving PET and also radioligand therapy with PSMA. For instance, the collaboration between UCLA and UCSF that brought to the FDA approval of gallium PSMA 11, and also the collaborations among the Australian group.

I’m looking forward to seeing many more collaborations if we come together. That’s the successful story of PSMA. I’m looking forward to seeing more of that.

Dr. Saji: Okay. That’s very exciting. For our last question, we kind of alluded to this earlier, when we were discussing the different half lives between the different radio isotopes, but it seems like the access to PSMA PET based imaging, it’s very regionally localized to specific areas of the country. Do you have any ideas on how we can expand access to PSMA based imaging to patients across the country, and then other nations where these types of nuclear medicine studies are harder to access?

Dr. Sonni: Yeah, I think it’s just a matter of time. If you think about it, PSMA was developed, the first clinical studies that were done with PSMA PET were in 2015. The first study that we did with the PSMA PET at UCLA was in 2016. We’re in 2022, we have already two PSMA PET radio pharmaceuticals that are approved by the FDA. It’s just a matter of time.

There are a few things that make me optimistic, in terms of making it more accessible and more widespread. For instance, recently, there was another approval for a kit that will allow the synthesis of gallium PSMA that would help produce this radio pharmaceutical more easily and distribute it more easily. There are a couple of things that make me really optimistic. For instance, in the US, this is relevant in the US, we received Medicare and insurance coverage, which is very important. That’s going to definitely change things.

Another really important aspect, I believe, is the approval rate from the clinicians. I see that there is a lot of excitement, a lot of interest, and a lot of hope from the clinicians: the urologists, the GU oncologists, rad onc, they’re really supporters of PSMA PET. A proof of that is the fact that the NCCN guidelines in 2022 incorporated PSMA PET in their guidelines.

When the clinicians support this imaging, I think that’s an important step that is only going to improve the widespread use. In the end, that’s what we’re looking for. We want this tool that we’ve worked on developing to be available for our patients, and that’s the overall goal. I think it’s just a matter of time, but it’s going to happen.

Dr. Saji: Okay. Thank you so much, Dr. Sonni. I really appreciate your time today. Thanks for taking the time to speak to us about PSMA PET imaging. We hope to interview you for other topics in the future.

Dr. Sonni: Thank you. It was a pleasure to be here. Thanks a lot.


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