At the 2018 American Society of Clinical Oncology (ASCO) Annual Meeting, promising results were reported from a phase 2/3 clinical trial testing the accuracy of a new prostate cancer imaging method — PSMA-PET — for detecting sites of prostate cancer recurrence.

The current standard imaging methods for detecting recurrent or metastatic prostate cancer are computed tomography (CT) and bone scans.  However, in many patients, these imaging methods are not sensitive enough to detect lesions early, when PSA levels first begin to rise (indicating that a patient’s prostate cancer is returning), or even to detect all lesions at any given time during disease progression.  More sensitive and more accurate prostate cancer imaging would enable earlier treatment of recurrent or metastatic disease, improve the accuracy of staging and prognosis, and could improve patient outcomes.

PSMA-PET is a new imaging technology that has been found in numerous early studies to be superior at detecting prostate cancer compared with CT and bone scans.   PSMA (prostate-specific membrane antigen) is a protein that is present at high levels on prostate cancer cells, and is an ideal target for both imaging and therapy.  In PSMA-PET imaging, a molecule that specifically binds to PSMA is attached to a radioactive atom that can be detected by the PET imaging machine.  Two different PSMA-PET imaging agents have progressed to testing in phase 2/3 clinical trials, 68Ga-PSMA-11 and 18F-DCFPyL.

Dr. Wolfgang Fendler, of the University of California Los Angeles (UCLA), reported results from a phase 2/3 clinical trial testing 68Ga-PSMA-11 PET plus CT imaging in 250 patients experiencing a rising PSA after previous treatment with radical prostatectomy or radiation therapy.

68Ga-PSMA-11 PET/CT imaging detected at least one lesion in 79% of the patients, including in 41% of patients with PSA levels <0.5 ng/ml, and increasing to over 80% of patients with PSA levels ≥ 1 ng/ml and nearly 100% of patients with PSA levels ≥ 5 ng/ml.  In 33 patients, surgery or biopsy on the lesions detected by PSMA-PET imaging confirmed 85% of these to be prostate cancer (85% accurate).  When other methods of confirmation were additionally assessed, accuracy was found to be as high as 91%.  In 23 patients, salvage surgery or radiotherapy was used to treat sites identified on PSMA-PET imaging, of whom 78% had a PSA drop of 50% or more, and 30% had PSA decreases to undetectable levels.

Overall, this study demonstrates high sensitivity and accuracy of 68Ga-PSMA-11 PET/CT imaging for prostate cancer.  Whether or not earlier detection of lesions using PSMA-PET imaging will improve patient outcomes is still under study and several ongoing clinical trials are addressing this question.

The results from this study will be submitted to the FDA, and will likely result in approval of this new prostate cancer imaging method in the near future.

The Prostate Cancer Foundation has been funding studies surrounding the development of PSMA-PET imaging for over twenty years.

Dr. Andrea Miyahira has a PhD in cancer immunology, and is Director of Research at the Prostate Cancer Foundation.