From the Desk of the Associate Editor: PSMA PET/CT in the Assessment of Intra-Prostatic Prostate Cancer

A large number of studies on 68Ga PSMA PET/CT are coming out of Australia due to the ready access to this technology.  To give some background, PET/CT imaging has long been registered with the Australian Therapeutic Goods Administration (TGA) and with this has come the approval to use any radionuclide tracer.  With it being unnecessary to apply for additional registration to use new tracers, this has allowed uptake of 68Ga PSMA PET/CT into routine clinical practice throughout Australia and to the extent that it is rapidly replacing conventional radionuclide bone scans and CT scan of the abdomen and pelvis as imaging for the staging of prostate cancer. 

Much of the focus of 68Ga PSMA PET/CT imaging has been with the detection of recurrence following the treatment of the primary disease or as a staging tool for the detection of metastases in newly diagnosed prostate cancer.  More recently, there has been a growing interest in the role of 68Ga PSMA PET/CT as a tool for the evaluation of intra-prostatic prostate cancer. 

This Australian study published in Prostate Cancer and Prostatic Diseases is one of a number of studies that are now evaluating the potential role of PSMA PET/CT in the assessment of intra-prostatic prostate cancer.  The study population is a highly selected cohort of subjects where a radical prostatectomy has been performed but prior to surgery, imaging with a multiparametric MRI scan of the prostate as well as a 68Ga PSMA PET/CT scan. Accordingly, it was possible to examine the pathological findings on the radical prostatectomy specimen in conjunction with findings on imaging.  A key finding of the study was that the index lesion on the radical prostatectomy specimen was able to be identified by the Ga68 PSMA PET/CT in all 50 cases but in only 47 cases with MRI. Additionally, PSMA had better sensitivity for index lesion localization than MRI (81.1 vs. 64.8% ) although there was similar specificity for PSMA PET/CT and MRI (84.6 vs. 82.7%).

This study provides yet further incremental support for PSMA being superior to MRI for the detection of intra-prostatic prostate cancer and in this cohort a 100% correlation with the index lesion on histopathology. Before we get too excited by this finding, further work needs to be done on a much wider population of subjects.  The reasons why a 68Ga PSMA PET/CT was performed in these men is not clearly stated, but it is highly likely that this was influenced by the results of histological grading on prostate biopsy. The necessary study cohort that needs to be evaluated is where undertaking a Ga68 PSMA PET/CT is not guided by biopsy pathology results but where the scan is a planned local disease evaluation study prior to prostate biopsy.

Whilst not the primary focus of this study, it was disturbing that in only one of six subjects with the suspected pelvic nodal disease had histological confirmation at pelvic lymph node dissection. This casts some reservations on just how much we can rely upon GA68 PSMA PET/CT findings.

It would be a provocative suggestion that we could one day take selected men direct to radical prostatectomy without a prostate biopsy on the basis of Ga68 PSMA PET/CT with or without MRI.  Studies such as this demonstrate a real potential for Ga68 PSMA PET/CT to have an important role in the future evaluation of the local disease for prostate cancer and perhaps even negate the need for prostate biopsy in selected cases.

Read the PCAN Full-Text Article: 68Ga-PSMA PET/CT vs. mpMRI for Locoregional Prostate Cancer Staging: Correlation with Final Histopathology

Written by: Henry Woo, MD, Associate Editor, Prostate Cancer and Prostatic Diseases, University of Sydney
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