18F-rhPSMA-7.3 lays the foundation for better PSMA-PET imaging techniques in prostate cancer

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Results from the Phase 3 SPOTLIGHT trial showed that 18F-rhPSMA-7.3 increased post-scan disease progression in recurrent prostate cancer.

At 2022 Annual Meeting of the American Urological Association, results from the Phase 3 SPOTLIGHT trial (NCT04186854) were presented on the use of 18F-rhPSMA-7.3 for PET/CT imaging in patients with recurrent prostate cancer. Its use has successfully led to better post-baseline disease staging compared to standard imaging.

Mark T. Fleming, MD, Medical Director of the U.S. Oncology Genitourinary Research Committee, Division Chief of the Department of Hematology and Oncology at Eastern Virginia Medical School, Chair of Medical Staff at Sentara Hospital Careplex, and Principal Investigator of the study, discussed the development of 18F-rhPSMA-7.3 and the need for a prostate-specific membrane antigen (PSMA) PET imaging agent like it.

“Based on my experience in this lawsuit as well as other [PSMA-PET] options available, I no longer get conventional imaging. Tome, [PSMA-PET] changed the field in that we detect localized disease,” Fleming said.

In an interview with CancerNetwork®, Fleming talked about the results of SPOTLIGHT, how this imaging agent may impact the standard of care, and where he hopes to see future research headed.

What was the rationale for developing the 18F-rhPSMA-7.3 imaging agent?

rhPSMA-PET takes advantage of the importance of prostate-specific membrane antigen in prostate cancer. It is evolving both as a diagnostic and potentially therapeutic modality. Conventional imaging, bone scans, and CT scans are simply not sufficient to determine early biochemical recurrence in patients with prostate cancer. It is a high affinity PET radiopharmaceutical, which has the advantage of having a low bladder activity as well as a longer half-life. From a production point of view, [it also has] greater lot potential.

What were the results of using 18F-rhPSMA-7.3 in the SPOTLIGHT trial?

The SPOTLIGHT trial involved men with prostate cancer who were treated with curative intent for localized disease. They had evidence of biochemical recurrence and were eligible for salvage therapy with curative intent. Imaging was performed with the rh-PSMA-PET scan. Importantly, the confirmation of the PET results showed a standard of truth – which was either histopathology, i.e. biopsy, or conventional confirmatory imaging – to confirm whether there is had signs of illness. There was an exploratory analysis of the effectiveness of true positive analysis which led to reclassification of patients with negative baseline imaging and there were approximately 250 patients in the group.

A detection rate examines the percentage of positivity of a study. More importantly, in this study, we looked at the correct detection rate which is a percentage of all patients who were scanned with at least one true positive PET result, confirmed by this standard of truth. This standard of truth was either biopsy or confirmatory imaging. When we look at this study, the correct detection rate was 45% to 47%, based on the 3 readers outclassing the patients. It is important to emphasize that these patients had an increase in their [prostate-specific antigen levels] and they had negative conventional imaging when we did the study. We were able to find a corrected detection rate of 45% to 47%, and this varies depending on the previous treatment as well as the anatomical region.

What are the next steps in agent development and when do you expect it to be available for daily practice?

The data is compelling that rh-PSMA PET is an attractive modality to detect biochemical recurrences and treat patients earlier. That’s what it’s all about, being able to create options for patients. How would you use it? If I see a site of disease, with rh-PSMA-PET, I might consider either surgical resection or targeted radiation therapy to the oligometastatic sites of disease.

The other additional element of rh-PSMA-PET is that it has the ability to potentially label α and β radio emitting patterns for systemic radiotherapy. Based on this, it has the advantage of being able to potentially combine this rh-PSMA-PET modality with future treatment options.

Is there anything else you would like to discuss?

The SPOTLIGHT study highlights what I consider to be a paradigm shift with its multidisciplinary use in prostate cancer. We are going to need radiologists able to read the PSMA-PET [scans] and have experience with PET scans. You must work with a urologist, a radiation oncologist and a medical oncologist. For me, when we collaborate and work together on behalf of our patients, we should use multidisciplinary care. Where we are in prostate cancer treatment in 2022 is a multidisciplinary field that is both diagnostic and therapeutic.

Reference

Fleming MT. Impact of 18F-rhPSMA-7.3 PET on the rehabilitation of patients with prostate cancer recurrence: results of the prospective phase 3 multicentre SPOTLIGHT study. Presented at: AAU Annual Meeting 2022; May 13-16, 2022; New Orleans, LA. Abbreviated PLLBA-02.

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