Researchers at the 2020 ASTRO virtual Annual Meeting are touting a new study that demonstrates the ability of PSMA PET/CT to distinguish between localized and metastatic cases of high-risk prostate cancer.

Staging of the disease is currently done with the use of a CT scan, usually of the abdomen and pelvis, and a technetium bone scan. The authors say the findings of their post hoc analysis show the effective role that PSMA PET/CT plays in the management of high-risk prostate cancer. The title of the study is Impact of 68Ga-PSMA-11 PET/CT on Initial Staging of High-Risk Prostate Cancer Patients: Post-Hoc Analysis of a Prospective Single Center Experience on the staging impact of PSMA PET/CT in men with NCCN high-risk prostate cancer.

“Conventional imaging for initial staging of prostate cancer (PCa) lacks sensitivity and underestimates disease burden,” said the authors in their study. “Prostate-specific membrane antigen PET/CT (PSMA PET) is an emerging imaging modality shown to have improved sensitivity over conventional imaging in the setting of biochemical recurrence.”
The study evaluated 249 patients with NCCN high/very high risk PCa who underwent PSMA PET imaging in a prospective trial between December 2016 and January 2020. PSMA PET upstaged 22.9% of patients, with 18.9% who were diagnosed with iN0 disease by CT or MR found to have N1 disease, and 10.6% given an M0 disease status by CT or bone scan now given an M1 disease status. Meanwhile, 7.4% received a new M1a disease and 5.3% were found to have M1b/M1c disease. In addition, PSMA PET detected ECE (the local spread of cancer beyond the prostate), seminal vesicle invasion or invasion of surrounding structures in 8.1% of patients ranked as T2 on prior MR imaging.

Those with a grade group of five or percentage of positive biopsy cores (PPC)≥50% were more likely to have regional nodal upstage and any upstage in general, while patients with GG 5 together with ≥50% PPC were predicted to have M stage upstage. cT and iPSA were not associated with upstaging.

While increasing in availability worldwide due to its higher sensitivity and specificity over conventional imaging, PSMA PET/CT is still limited in use, including in the U.S. where the FDA has not yet approved the agent.

Overall, PSMA PET/CT identified 19.7% of patients with regional PET positive nodal disease and 9.4% with metastatic disease on PET/CT. While not uniformly biopsy-proven areas for metastatic disease, it is possible based on prior research that 85%-98% of lesions found in these areas are likely to be prostate cancer, according to Dr. Daniel Spratt, a radiation oncologist at the University of Michigan who saw the presentation. He adds that the findings show that GG 5 (Gleason Score of 9-10) and >50% of biopsy cores involved with cancer predicted for non-localized prostate cancer.

“Based on clinical trials led out of UCLA, UCSF and other centers, I am hopeful that these molecular imaging modalities can soon be added to our toolbox to better personalize our treatments,” wrote Spratt in an ASTRO op-ed.

The findings were published in the International Journal of Radiation Oncology · Biology · Physics.

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