Main Session
Sep 30
QP 15 - GU 8: Quick Pitch: Novel Concepts in Localized Prostate Cancer

1086 - Identifying Optimal Candidates for PSMA PET Staging of Newly Diagnosed Intermediate Risk Prostate Cancer: A Report from the National Veterans Affairs System

05:30pm - 05:35pm PT
Room 156/158

Presenter(s)

Joseph Tang, MD - University of Michigan, Ann Arbor, MI

J. D. Tang1, S. R. Miller2, M. Schipper2, W. C. Jackson2, K. D. Stensland3, M. E. Caram4, P. A. Tsao4, D. A. Elliott1, R. T. Dess2, and A. K. Bryant1; 1Department of Radiation Oncology, Veterans Affairs Ann Arbor Health System, Ann Arbor, MI, 2Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 3Section of Urology, Veterans Affairs Ann Arbor Healthcare System, Ann Arbor, MI, 4Division of Medical Oncology, Department of Medicine, Veterans Affairs Ann Arbor Healthcare System, Ann Arbor, MI

Purpose/Objective(s): Current NCCN guidelines endorse PSMA PET staging for newly diagnosed patients with unfavorable intermediate risk (UIR) prostate cancer. However, the rate of PSMA-positive findings in this group remains unclear, raising questions about whether universal use of this costly modality is justified. This study leverages the largest cohort to date of intermediate risk prostate cancer patients to more accurately determine PSMA positivity rates, identify key predictors of positivity, and assess whether a prediction model can more efficiently select patients for PSMA staging.

Materials/Methods: We retrospectively identified all patients diagnosed with favorable intermediate risk (FIR) or UIR prostate cancer within the national Veterans Affairs system from 2015 to 2024 who underwent PSMA PET staging within six months of diagnosis. Patients with indeterminate or positive conventional imaging findings (CT, MRI, or Tc99m bone scan) prior to PSMA staging, as well as those with MRI-confirmed seminal vesicle invasion, were excluded. A physician reviewer manually annotated PSMA PET findings (nodal or distant metastatic involvement) from radiographic reports. Multivariable logistic regression was then used to identify predictors of PSMA positivity, considering demographics, Gleason score, percent positive cores, baseline PSA, clinical tumor stage, and PSMA PET tracer type (18F vs. 68Ga).

Results: After exclusions, 2,025 patients remained (FIR: n=311; UIR: n=1,714). Overall, PSMA positivity (N1 or M1) was observed in 4.2% of FIR patients (1.6% N1M0, 2.6% M1) and 5.9% of UIR patients (3.0% N1M0, 2.9% M1). In multivariable analysis, only baseline PSA (adjusted OR 1.48 per 5 ng/mL increase, 95% CI 1.19–1.83, p<0.001) and Gleason score (adjusted OR 1.53 for 4+3 vs. 3+4, 95% CI 1.03–2.31, p=0.038) were significantly associated with PSMA positivity, while age, race, clinical tumor stage, percent positive cores, and PET tracer type were not. A predictive model incorporating only PSA and Gleason score achieved an AUC of 0.62 (95% CI 0.56–0.67), with 88% of FIR patients and 42% of UIR patients exhibiting a predicted PSMA positivity risk below 5%.

Conclusion: In the largest study to date of intermediate risk prostate cancer patients undergoing PSMA staging, we observed lower positivity rates than previously reported. These findings suggest that universal PSMA staging in UIR prostate cancer may have limited clinical utility. A simple prediction model based on PSA and Gleason score could help safely reduce unnecessary PSMA staging in many lower-risk patients.