clinical topic updates
Imaging Techniques in Metastatic Prostate Cancer
Although their impact on oncologic outcomes should be better defined, next-generation imaging techniques such as gallium-68 (68Ga) prostate-specific membrane antigen (PSMA) positron emission tomography (PET) and 18F fluciclovine PET have been increasingly adopted into clinical practice. These tools can change treatment planning, and many clinicians expect that outcomes will improve accordingly.
Ken and Donna Derr – Chevron Distinguished Professor
“PSMA-based imaging will become the dominant form of next-generation imaging in this country, as it is around the world.”
The US Food and Drug Administration (FDA) recently approved PSMA PET imaging at the University of California, San Francisco (UCSF) and the University of California, Los Angeles, and based on that application, others will follow suit. Fluciclovine was previously approved for use in men who have a rising prostate-specific antigen following prior definitive therapy. The approval for 68Ga PSMA PET imaging included its use both at the time of diagnosis and at the time of recurrence. 68Ga PSMA has an FDA-approved indication for both uses. Even more recently, the FDA approved 18F-DCFPyL PSMA PET based on data from the OSPREY (NCT02981368) and CONDOR (NCT03739684) trials. In terms of imaging in metastatic prostate cancer, my sense is that PSMA-based imaging will become the dominant form of next-generation imaging in this country, as it is around the world.
We know that PSMA at either the time of diagnosis or the time of recurrence gives you unique information in a very large percentage of patients. That information results in changes to the treatment plan compared with planning based on conventional imaging. Whether those treatment changes will result in improved long-term outcomes is not yet known. We do believe that outcomes will be improved, and we are involved in clinical trials designed to study that question.
Our experience at UCSF suggests that, in the setting of definitive treatment failure, the treatment plan will change with PSMA-based imaging (compared with conventional imaging) in approximately 30% to 40% of cases. A driving factor for these changes is the detection of additional involved lymph nodes using PSMA—lymph nodes outside of the areas originally included in the treatment plan. Once such sites have been identified, if you are planning to administer radiation, you can include nodes that are not in the original field and boost the dose to sites of disease. Instead of giving 45 Gray, you can actually administer stereotactic radiation therapy to these sites. A study is underway (NCT03582774) that is comparing standard-of-care salvage radiotherapy to salvage radiation therapy planned with the benefit of PSMA PET imaging.
When PSMA imaging is performed either at the time of diagnosis or at the time of biochemical relapse, you most commonly identify regional or retroperitoneal disease, rather than metastatic disease. At UCSF, we found that only around 24% of the patients who had failed previous treatment and had a rising prostate-specific antigen had bone or visceral metastases, but a rather substantial number had regional or retroperitoneal disease. Thus, another facet of next-generation imaging is its role in identifying oligometastatic disease. Patients with oligometastatic disease have metastases in relatively few sites (eg, 2-6 sites), and there has been a trend toward aggressive treatment in these patients. Instead of using systemic therapy alone, one might employ systemic therapy plus stereotactic body radiation and, in some cases, surgery. Again, we never knew that this whole new category of disease existed because we did not have the imaging tools that allowed us to detect it.
ClinicalTrials.gov. Multicenter randomized trial of 68Ga-PSMA-11 PET/CT based SRT after radical prostatectomy (PSMA SRT). Accessed June 23, 2021. https://clinicaltrials.gov/ct2/show/NCT03582774
ClinicalTrials.gov. Study of 18F-DCFPyL PET/CT imaging in patients with prostate cancer (OSPREY). Accessed June 23, 2021. https://clinicaltrials.gov/ct2/show/NCT02981368
ClinicalTrials.gov. Study of 18F-DCFPyL PET/CT imaging in patients with suspected recurrence of prostate cancer (CONDOR). Accessed June 23, 2021. https://clinicaltrials.gov/ct2/show/NCT03739684
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