ESTRO 2024 - Abstract Book

S2539

Clinical - Urology

ESTRO 2024

(regional nodes and distant metastases) or distant metastases. The R statistical software, including the rms package was used for analysis.

Results:

The patient cohort was predominantly comprised of patients with more than one high risk feature. The median PSA value at diagnosis was 21.26 ng/dl (IQR 11.54 - 43.53 ng/dl). Gleason grade group 4 or 5 was present in 110 (56.7%) patients. Multiparametric MRI based T3 disease was present in 139 (71.3%) and T4 disease in 15 (7.7%). High risk prostate cancer using NCCN criteria (prior to staging PSMA PET-CT) was seen in 181 patients (92.34%). Extraprostatic disease was detected on PET-based staging in 84 (42.8%) and distant metastatic disease in 36 (18.4%). Among patients with distant metastases extrapelvic nodal disease was seen in 18(9.2%), skeletal uptake was seen in 17 patients(8.7%) and visceral metastases in 8(4.1%) patients. When comparing patients with extraprostatic disease vs. prostate confined disease, we did not find a statistically significant difference in the initial PSA 23.52 vs. 20.34 (p = 0.19). There was a non-significant higher incidence of Gleason grade group 4 or 5 disease with 53 (63.9%) vs. 57 (51.4%) (p = 0.11). There was a significant difference in the incidence of T4 disease with 11 (13.3%) and 4 ( 3.6%) patients (p = 0.042). For patients with distant metastatic disease there was a lack of significant difference between all of the 3 predictor parameters under study. A logistic regression model for patients with extraprostatic disease as detected by the PSMA PET scan based on PSA, MRI-based T stage and Gleason grade- group showed a likelihood ratio χ2 of 12.78, R2 index 0.086, C index value of 0.633 and Pr(>χ2) value of 0.0255, with only moderate discrimination and calibration. Modelling for metastatic disease based on the same features yielded poor predictive ability with a likelihood ratio χ2 of only 4.76, R2 index 0.04, C index 0.57 andPr(>χ2) of 0.446.

Conclusion:

There was a high incidence of detection of both extraprostatic disease and distant metastases with Ga68 PSMA PET CT. However, there was a lack of robust discrimination or calibration with modelling based on PSA, T-stage and Gleason grade group, and clinically useful risk-stratification was not possible. In this population, all patients should continue to undergo staging scans with PSMA PET CT scan.

Keywords: PSMA-PET, Staging, Prostate