INTRODUCTION AND OBJECTIVE:
68Ga-labeled prostate-specific membrane antigen (PSMA) positron-emission tomography (PET) computed tomography (CT) imaging quickly earns an important role in staging radical prostatectomy candidates. While PSMA is generally weakly expressed in normal prostate tissue, it is strongly upregulated in prostate cancer. However, some clinically significant prostate cancers exemplify low reads on PSMA PET CT. In the current work we evaluate this unique sub-population of patients with ‘negative’ prostate PSMA PET CT reads.
We retrospectively reviewed 392 patients who underwent radical prostatectomy between September 2014 to July 2019 in 5 medical centres.Patients with pre-operative PSMA PET CT imaging were included. We collected data on baseline characteristics including demographics, comorbidities, prostate specific antigen (PSA) and rectal exam, prior biopsies, imaging results, and biopsies and radical prostatectomy histology. An index group of patients with ‘negative’ PSMA PET CT prostate read was defined as “scarce” uptake and/or numerically maximal standardized uptake value (SUVmax) below physiologic uptake. For control we used patients with PSMA PET CT prostate read defined as “intense” and/or numerically as SUVmax above physiologic uptake.
97 patients had PSMA PET CT imaging prior surgery, 52 (54%) of whom fitted with the index group inclusion criteria and 45 (46%) with the control group. All pre-operative characteristics did not significantly differ in-between groups except lesion size and SUVmax per PSMA PET CT (Table1). Prostatectomy specimen’s histology analysis significantly differed in-between groups, for ISUP score, seminal vesicles invasion, T stage and positive margins rates (p<0.05).Nonetheless, 50 (96%) of the index group patients harbored clinically significant disease (ISUP>=2) with extra-prostatic disease showed in 24 (46%) and peri-neural invasion in 35 (67%).Positive lymph nodes were found in 4 (8%) of index group patients.
While prostate cancer aggressiveness was generally correlated with intense uptake of PSMA on pre-operative PSMA/PET CT, a subpopulation of patients with clinically significant cancer and aggressive characteristics show weak reads only on this imaging. These data raise concern applying PSMA PET CT for staging of prostatectomy candidates.
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