Competition (‘steal’ phenomenon) betwe en [68ga]ga‐psma‐11 uptake in prostate tumor tissue versus healthy tissue

Abstract

We aimed to clarify whether a steal ‘phenomenon’ exists by investigating if uptake of ‘prostate specific membrane antigen’ (PSMA) in prostate tumor tissue correlates with the uptake in healthy tissue. Patients with prostate cancer referred for a [68Ga]Ga‐PSMA‐11 PET/CT were identi-fied retrospectively. Semi‐automated quantitative image analysis was performed; fractional healthy tissue [68Ga]Ga‐PSMA‐11 uptake volume (HT‐PSMA (SUV*cm3)) in the lacrimal, submandibular, and parotid glands, and kidneys, and the fractional total lesion [68Ga]Ga‐PSMA‐11 uptake volume (TL‐PSMA (SUV*cm3)) of prostate cancer were used. Ninety‐two patients, age 78 ± 8 years, were analyzed. Median TL‐PSMA was 703.37 SUV*cm3 (IQR 119.56–2778.20), median HT‐PSMA of the lacrimal, submandibular, and parotid glands, and kidneys was: 13.69 (IQR 7.29–19.06), 194.75 (IQR 133.67–276.53), 552.54 (IQR 379.98–737.16), and 8092.75 SUV*cm3 (IQR 5793.02–11385.86), respec-tively. A significant (p‐value ≤ 0.001) but weak–moderate correlation was found between the TL‐ PSMA and HT‐PSMA of the parotid‐ and submandibular glands, and kidneys (correlation coeffi-cient of −0.447,−0.345, and −0.394, respectively). No correlation was found between TL‐PSMA and HT‐PSMA of the lacrimal glands. The existence of a ‘steal’ phenomenon cannot be confirmed in this study. Healthy tissue uptake of [68Ga]Ga‐PSMA‐11 is only partially influenced by TL‐PSMA. Thus, modification of therapeutic PSMA activity should not be adjusted based on TL‐PSMA alone.