GU Oncology Now: What is the impact of PSMA imaging in the detection of prostate cancer?

Dr. Jeffrey Karnes: Thank you for the question. I do believe that the PSMA scan will be a game changer as it comes to prostate cancer, I think mainly in the field of recurrent prostate cancer. It’s certainly been studied and evaluated also in the diagnostic or the staging realm of prostate cancer, i.e., detection.

So there’s been a really nice study done called the proPSMA study, where they looked at patients who were undergoing staging prior to like a definitive therapy, and the accuracy of PSMA over what we consider conventional imaging like a bone scan and a CT scan. It was greater than 25% more accurate in the detection of spread of the prostate cancer. Additionally, there were some more equivocal findings with conventional imaging over the PSMA imaging.

Where I really think a nice feature of the proPSMA study that was published in Lancet just a year ago, was that almost a doubling… But for a patient that had a PSMA-based image detected metastasis, the management changed by about twofold. Meaning about 30% of the time, PSMA led to a change in management compared to 15% of the time when patients had conventional imaging. It was a well-designed study. So that’s important in detection of spread prior to intervention.

But where I really think that PET imaging is going to revolutionize how we manage prostate cancer is in the recurrent setting, where we know that conventional imaging is poorer in detecting spread after curative intent whether radiation or surgery, and there was a PSA recurrence. We know from thousands and thousands of patients that, depending on the PSA level but at very low PSA levels, even less than 1, and sometimes at PSA levels of 0.2 in the postoperative setting, the PSMA PET can detect some metastasis, which the hope is by earlier intervention on those metastasis that we actually can impact outcomes of those men for the better obviously.

Describe the clinical benefits of 68Ga PSMA-11 access for a prostate cancer patient.

So, I’ve been heavily involved in the development of a C-11 Choline PET/CT scan for staging and re-staging of recurrent prostate cancer. It does require a on-site cyclotron, which is not readily accessible for most physicians and patients around the country. With PSMA, it will be a kit that could be sent to facilities that have our standard PET/CT capabilities. The standard PET/CT that is done for various malignancies is called FDG. It’s a glucose-based PET. But if they have that facility, then the PSMA kit, both the Gallium and the PSMA can be shipped to those centers and provided more access to patients from around the country.

How do you determine the right imaging procedure at the right time to provide better outcomes?

I’ll focus more on the recurrent prostate cancer study, whether it be a surgery or radiation. I certainly don’t think that PSMA PET/CT replaces an MRI. Certainly there’s some, I think, feasibility of getting MRIs, especially in patients who are failing via PSA of primary radiation therapy to look at the prostate in more kind of anatomical detail. That is obviously more granular than could be provided by a PSMA PET. Certainly, there are some PSMA PET MRI research going about, but I think an MRI and a PET/CT scan provides sort of the whole picture. I think what PSMA PET certainly can start at very low values of PSA [inaudible].

Currently, we have an ongoing study of starting a PSMA PET scan at a PSA of 0.2 post-operatively. Radiation has various definitions, but certainly I think once a patient meets that definition of radiation failure, then a PET scan is warranted as well as an MRI. But the performance accuracy of any PET scan and the performance accuracy of even an MRI is truly based on the PSA. So the lower the PSA, the less likely you are to detect metastasis. As the PSA climbs [inaudible], there has to be a finding.

If a patient has an extremely low PSMA levels or biochemically recurrent prostate cancer, how do you select the best imaging modality? 

So I truly think the concept of performing bone scans, performing CT scans for men with low PSA’s after prostate cancer surgery is going to go to the wayside. We are truly focusing our efforts on MRI and PSMA PET/CT scans or occasionally a choline scan still, depending on the patient’s histopathology and course. I think ultimately all of our hope is that by that earlier detection of recurrent disease or that earlier detection of metastasis, even a concept called oligometastases which are few metastasis, by earlier intervention, that we truly impact survival and outcomes that are an improvement of what we’ve seen in the past.

We know that, for instance, in the postoperative setting for men who have a PSA recurrence, by using a PET scan, there can be improved even post-operative radiation outcomes over conventional CT scans that have been historically performed to determine the radiation fields.

What would you leave as a take-home message for practitioners watching this interview?

As I mentioned earlier, even PET/CTs in general, I think have revolutionized how we manage men with recurrent prostate cancer. Perhaps now, even with initial staging of a particular high risk prostate cancer, I think that ultimately there’s ongoing research being done. I do think that a PSMA PET scan will become sort of our standard imaging as it pertains to recurrent prostate cancer. The hope is that by, as I mentioned, perhaps the earlier detection and earlier intervention, and definitely getting the PET scan on the right patient at the right time, and providing the right therapy will be a game changer.

I think that with the use of PET scans, sort of that’s fairly ubiquitous across other cancers in the US, it would be fairly standard for patients to get a PSMA PET scan across the country, as it pertains to either recurrent prostate cancer or even progressing metastatic prostate cancer, since PSMA can still be readily expressed in the majority of recurrent prostate cancers.