Standardized PSMA-PET Imaging of Advanced Prostate Cancer

Imaging of advanced prostate cancer is a challenging task, as it requires longitudinal characterization of disease extent in a standardized way to enable appropriate treatment selection and evaluation of treatment efficacy. In the last years, prostate-specific membrane antigen (PSMA)-PET/CT has become the reference standard examination for patients with advanced prostate cancer. Together with the rise of PSMA-PET, standardized frameworks for the reporting of image findings have been proposed, eg, the Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) and the structured reporting system for PSMA targeted PET imaging (PSMA-RADS) framework. Therefore, recent evidence on PSMA-PET derived tumor volume as useful a biomarker for outcome prognostication and related frameworks will be discussed in the article. The PROMISE framework recommends quantifying the tumor volume per-organ system, which accounts for the fact that the location of the metastases greatly influence its biological aggressiveness. In addition, changes in PSMA-PET derived tumor volume have been shown to be promising biomarkers for response assessment. Limitations of PSMA-PET will also be discussed because the tumor volume might not always be suited for response assessment. As a pitfall of PSMA-based systems, decreasing PSMA-expression might erroneously be interpreted as response to therapy. Also, especially for patients with limited disease, the tumor volume might not be ideal for response assessment. Therefore, various frameworks have been introduced to objectively measure response to therapy with PSMA-PET. Amongst these, the PSMA-PET progression (PPP) criteria and the response evaluation criteria in PSMA (RECIP) are optimized for earlier and later phenotypes of advanced prostate cancer, respectively. Variables needed to determine PPP or RECIP outcome on PSMA-PET are recorded under the umbrella of PROMISE recommendations. In this article, various reporting and response assessment frameworks are explained and discussed. Also, recent evidence for the relevance of PSMA-PET biomarkers for clinical management and outcome prognostication are shown.