PSMA expression by PET (PSMA-positive)

Overview

• Where PSMA sits in the body, from the tissue survey the imaging rests on: detectable in prostatic epithelium, duodenal mucosa, a subset of proximal renal tubules and colonic neuroendocrine cells, and undetectable in every other normal tissue including cerebral cortex and cerebellum; present in 33 of 35 primary prostate adenocarcinomas and 7 of 8 nodal metastases but only 8 of 18 bone metastases, with expression falling as tumours dedifferentiate (Silver 1997).
• What the scan changes at staging: in 302 men randomised before curative-intent treatment, PSMA PET-CT was 27% more accurate than CT with bone scan, 92% against 65%, with sensitivity 85% against 38%, management change in 28% against 15%, fewer equivocal findings, 7% against 23%, and less radiation, 8.4 against 19.2 mSv (Hofman 2020).
• What it changes at biochemical recurrence: recurrence was localised in 475 of 635 men, 75%, with detection rising from 38% below PSA 0.5 ng/mL to 97% at 5.0 or above, and positive predictive value 0.84 by histopathology (Fendler 2019).
• How many men it excludes from radioligand therapy: of 291 men screened for TheraP with PSMA and FDG PET, 200, 69%, were eligible, the rest excluded for PSMA-low disease or FDG-positive PSMA-negative sites (Hofman 2021).