Reactions to key findings from an article by Birgit Pernthaler, et al, that compared the use of 18F-fluciclovine with 68Ga-PSMA-11 imaging modalities to detect biochemical relapse in prostate cancer.
Steven Finkelstein, MD, DABR, FACRO: As we get into some of the key takeaways from the paper, we’ll talk about some of the conclusions. The first was the advantage of 18F-fluciclovine in detecting curable localized disease in close anatomic relation to the urinary bladder, whereas gallium PSMA [68Ga-PSMA-11] fails because of accumulation of activity in the urinary bladder. However, 18F-fluciclovine is almost equivalent to 68Ga-PSMA-11 in detecting distant sites of prostate cancer. As we talked about on the previous slide, for most situations outside the urinary bladder area, 68Ga-PSMA-11 was superior. What key points resonate with you from this paper, Louis?
Louis J. Mazzarelli, MD: You asked about some nuance to reading it. That’s something that needs to be considered when we’re thinking about these radiotracers, because 1 radiotracer we believe outperforms the other when it comes to outside the bed. When we want to question the bed, 1 thing we need to do for any future study—we’ll talk about that when we think about things—is optimization of technique. How would we optimize gallium-68 or F18-fluciclovine PSMA [prostate-specific membrane antigen] to perform better locally? I can speak anecdotally. To optimize the ability to identify disease locally with PSMA, 1 thing you do is acquire images as some institutions have, like my own, beginning with the thighs going toward the vertex. You decrease the amount of radioactive tracer within the bladder. From a PSMA perspective, you also have the patient void when they come to the imaging facility and have the patient void right before getting onto the scanner. Those are 2 other things you can do to optimize the ability to visualize the prostate.
The other thing you need to do when you’re looking at these scans—and this is true when it comes to 18F-fluciclovine, from the ability to look at bone and with a nodal disease—is windowing. Windowing is crucially important. Everything in PET [positron emission tomography] is about background. If your background in the bladder is incredibly high, you’re not going to be able to see anything next to it. But if you’re able to window the bladder appropriately, you’ll have a higher likelihood of identifying local disease. One thing I was wondering about—Steve, I don’t know if you wondered this as well—is that I don’t believe the paper broke down the amount of local recurrence identified by prostatectomy vs radiation therapy. We have a number of patients we saw who had recurrent disease locally at the bed, but it wasn’t clear to me which number of patients were from the radiation therapy side vs the prostatectomy side.
Steven Finkelstein, MD, DABR, FACRO: Their numbers were so small that they were concerned that if they broke it in subset analysis down to such low numbers, they would not have favorable reviewing on the paper. Fifty-eight was obviously the largest series when this paper was published, and that in 2019. Obviously, there’s a lot more interest and a lot more availability of gallium-68 scanning in the way of PYL [18F-DCFPyL] PET, and you would imagine that there will be some United States–based publications doing this work. The limitation previously had been where you could get gallium scans. With the advent of doing PYL scans, you’d imagine that you might have some subset papers of postprostatectomy and postradiation therapy, and be able to tease out some of these answers about the differences between 18F-fluciclovine and PSMA PET to detect recurrences in prostate cancer.
Transcript edited for clarity.