Sensitivity of Imaging Modalities to Biochemical Recurrence in Prostate Cancer
Dr Munir Ghesani reviews and comments on data regarding the sensitivity of imaging modalities in detecting biochemical recurrence in prostate cancer.
Raoul S. Concepcion, MD, FACS: Dr Ghesani, let’s make a hypothetical situation here. Assuming you had access to both fluciclovine and PSMA [prostate-specific membrane antigen], are there any data out there to suggest that at lower PSA [prostate-specific antigen] levels, one modality may be superior? Is it in general, or is one better than the other for soft tissue versus bone?
Munir Ghesani, MD: First, there is significant published literature on the linearity of PSA levels correlating with the fluciclovine PET [positron emission tomography]/CT. As the PSA levels increase, the sensitivity of fluciclovine goes up. What is also interesting is that in some of those studies they looked at, even when the PSA level was less than 1 [ng/mL], there was still a significant number of cases where the Axumin [fluciclovine] picked up the disease. And in that subgroup of patients, CT and bone scans were completely negative.
To answer the question, no level of PSA is too low for these imaging modalities to show superiority with fluorine- or gallium-based PET scans [compared with] CT and bone scans. If at any point there is a concern, and it’s a clinical question, as Judd mentioned, that this patient does not meet the absolute definition, but the doubling time and then the nadir was not low enough, so there is a high degree of suspicion. In that case, if the insurance companies don’t give you pushback, then clearly the fluciclovine scan will be appropriate. Now, there are some emerging data that have shown, and it’s still early stage, that PSMA scans behave the same way, that as the PSA levels increase, their sensitivity starts to go up. There is at least 1 study that has looked at comparing the 2 and showing some superiority of gallium PSMA scans over the fluciclovine in the setting of very low PSA levels. Again, you must balance that with availability of the agents. Let’s say only fluciclovine PET is available, it still would be very appropriate to do that scan because studies have shown that it performs better than CT and bone scans in that setting.
Raoul S. Concepcion, MD, FACS: Are there any data to suggest that the PSMA or the fluciclovine performs better in soft tissue? Does one perform better than the other, or vice versa in soft tissue versus bone? Or is it equal in terms of detection?
Munir Ghesani, MD: There are still very early data, but they both do very well. What I have seen in my experience—these are not published data, and this has been referenced in some other ways—is that when you do the fluciclovine PET, you usually scan the patients about 3 to 5 minutes after injection. This means that the prostate bed is generally devoid of any urinary excretion, and that’s an advantage because in molecular imaging, you’re always looking at higher target and a lower background. If you lower your background in any specific way, then you are going to pick up things that are even subtle relative to a high background. In that case, the fluciclovine technically can have superiority when you’re looking at recurrence in the prostate bed. Many of the PSMA scans are done at a later stage, and there is invariably some degree of urinary excretion, so the bladder activity can obscure any small area of recurrence technically, that can be only in the prostate bed.
Transcript edited for clarity.
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