Assessment of biological tumor volume – a relevant prognostic parameter in metastatic prostate cancer?

Ziel/Aim Whole body metabolic tumor volume and total lesion glycolysis are biomarkers for assessing FDG-PET scans of patients suffering from various malignancies. However, little is known about the prognostic potential of whole-body PSMA-derived tumor volume (PSMA-TV) and whole-body total lesion PSMA (PSMA-TL) derived from ⁶⁸Ga-PSMA PET/CT in patients with recurrent prostate cancer (PCa), especially those receiving chemotherapy. It remains unclear whether different software algorithms influence PSMA-TV and PSMA-TL results and wether these calculations provide prognostic information.

Methodik/Methods ⁶⁸Ga-PSMA I&T-PET/CT scans from n = 22 castration-resistant PCa (CRPC) patients receiving Docetaxel or Cabazitaxel for systemic treatment were identified within a single-center database. All patients had at least one PET/CT scan before and after completion or termination of systemic chemotherapy. We calculated PSMA-TV and PSMA-TL for all PET/CT scans with Syngo.via software (Siemens) as well as Beth Israel plugin for FIJI. Serum PSA levels were determined before and after administration of chemotherapy. PERCIST criteria were applied for assessing individual signal alterations in the course of chemotherapy. Kaplan-Meier analyses were used for assessing the prognostic potential of biochemical response (BR), PERCIST, PSMA-TV and PSMA-TL.

Ergebnisse/Results Calculation of PSMA-TV and PSMA-TL did not differ significantly between the two software applications used (baseline and follow-up). Significant correlations were seen between baseline and follow-up PSMA-TV, PSMA-TL and PSA levels as well as between ΔPSMA-TV, ΔPSMATL and ΔPSA. Significantly longer survival was reported for PCa patients with a lower tumor burden at baseline. Regarding therapy response, only BR indicated significantly longer survival in responders, whereas PERCIST, ΔPSMA-TV and ΔPSMA-TL did not.

Schlussfolgerungen/Conclusions ⁶⁸Ga-PSMA-PET-derived PSMA-TV and PSMA-TL significantly predicted survival of PCa patients receiving taxane-based chemotherapy. However, both biomarkers could not outperform BR and PERCIST for therapy monitoring in terms of predicting overall survival.