Gallium-68 PSMA Targeted PET Imaging in Prostate Cancer: Staging and Outcomes - Episode 3
Andre Abreu, MD, discusses the rationale behind targeting PSMA (prostate-specific membrane antigen) and its impact on the patient journey from diagnosis to biochemical recurrence.
Phillip Kuo, MD, PhD: If I could get your input, Dr. Abreu, on how you feel—you’ve already touched upon this—how will it impact the patient journey from diagnosis? As we know, it inevitably recurs in some patients, there is a biochemical recurrence, and then forward.
Andre Abreu, MD: That is a very good point and a good question. The PET [positron emission tomography] PSMA ]prostate-specific membrane antigen] scan should have a role and should have a place in every aspect of prostate cancer treatment, from diagnosis to staging, to restaging or recurrence, and even for evaluation of the treatment afterward, in terms of if there is disease regression or not. Going through the diagnosis, this is mostly what I do. When we use the PSMA by itself, because the CT scan is not a very refined imaging for the prostate, there are a lot of limitations. For example, when we do the PET PSMA, we can localize the disease. We know it is within the prostate, but when we try to biopsy—we have done some trials on this—because of the definition of the imaging of the CT scan itself, it is not that good. We may not identify, may not target appropriately that way. When we combine PET CT with MRI scans, then we have a win-win; we gain both image modalities. We get all the aspects of the T [tumor] stage for the MRI with disease localization. We get the PET CT on top of it, which can even identify other lesions that the MRI did not, with the benefit of scanning the entire body. Should we do this for every single patient? This is the question. The fusion of PET CT, and MRI scans in itself costly; some machines are available but they have a cost.
However, if we do both separately, this could be beneficial and feasible for fusion biopsy, PET CT, MRI, and ultrasound. This is one aspect. Our question is: should we do this for everybody? Cost is an issue, but cost usually decreases with time. The second aspect is the staging, as we discussed. As we get good T staging with the MRI, then we can have appropriate staging with the PET CT or the PET PSMA. Then, we can identify, and better risk stratify. We can deliver appropriate treatment for these patients. Then the patients are treated. Afterward, it depends on the risk of the patient; 15% to 20% of them, or even more, would typically have a recurrence. This is an example of the most specific need for PET PSMA currently. That’s why it was approved, there is a lot of research on it, and for localization and management of these cases. If the disease is indeed localized after prostatectomy, the disease is in the prostatic bed, depending upon if there is nodal disease or not. It is similar for radiation therapy; depending on the biochemical recurrence, the PET PSMA can do better or not. Again, this may possibly exclude diseases outside of the prostate, like metastases, or nodal disease, so this can then impact the management.
One aspect that is very interesting and unique for the PET CTs, especially in the case of PET PSMAs, is the concept of patients with nodal recurrence only after prostatectomy. There was excitement for this patient population that we could potentially do a radical prostatectomy for them or we would do a salvage lymphadenectomy for them, and they would do better. Then, with the [data] series maturing and longer follow-up, we see that this is not the case. But we can certainly say that patients who have lymph node metastases to the pelvis only tend to do better than those who have disease to the retroperitoneum, when we do the retroperitoneal nodal dissection.
In our series here, from USC [the Keck School of Medicine at the University of Southern California], which is a large series with many lymph node dissections, led by [Inderbir Singh] Gill, [MD,]—we identified that there are some skip sections. That means if the patient has disease at the pelvis, and you dissect all the way up…if there is a gap, these patients might still have disease within the retroperitoneal area. We just do not know. When we do the PET PSMA, we can better identify these patients. They have truly only 1 nodal invasion close to the pelvis. These patients would be better candidates for surgery or for whatever treatment you want to use for them, like radiation for that specific area. Again, the PET PSMA plays a role. We need more research on this, but it looks like it will be beneficial for the entire spectrum of patients with prostate cancer.
Transcript edited for clarity.