3359 - Timing of Molecular PET Imaging after Salvage Radiation Therapy for Recurrent Oligometastatic Castration-Sensitive Prostate Cancer

12:45pm - 02:00pm PT

Hall F

Screen: 27

POSTER

Presenter(s)

Jarey Wang, MD, PhD - Johns Hopkins University School of Medicine, Baltimore, MD

J. Wang¹, A. C. Shetty², Y. Song², X. Shi², N. Radwan², D. Song¹, T. L. DeWeese¹, M. P. Deek³, H. C. Onal⁴, L. Ren², A. P. Kiess¹, P. T. Tran², and P. Sutera⁵; ¹Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, ²University of Maryland School of Medicine, Baltimore, MD, ³Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, ⁴Department of Radiation Oncology, Baskent University Faculty of Medicine, Adana, Turkey, ⁵University of Rochester, Rochester, NY

Purpose/Objective(s):

Advanced molecular PET-CT imaging is typically obtained due to rising PSA after radical prostatectomy (RP) and salvage prostate bed/pelvic radiation therapy (SRT) in order to characterize the extent of disease. However, the threshold of PSA to define biochemical recurrence (BCR) after SRT and the optimal timing of molecular PET imaging (MPI) in relation to PSA remains unclear. We sought to investigate the relationship between PSA and timing of detectable recurrent oligometastatic disease (OMD), as well as any associations with clinical and genomic tumor features.

Materials/Methods:

This retrospective study included men who had initial oligometastatic progression detected on MPI after SRT between 2016-2021 and who also had primary tumor DNA sequencing. PSA at time of OMD detection was considered as a continuous variable for Cox regression analysis of progression free survival (PFS). Timing of MPI was also stratified based on the Phoenix definition of PSA rise of =2 ng/mL above the post-SRT nadir and defined as either Ph+ (meeting criteria) or Ph- (not meeting criteria). Molecular PET agents included DCFPyL, choline, and fluciclovine. DNA sequencing of primary tumor was performed via FoundationOne CDx, Tempus xT, or PGDx. Assessment of differences in clinical and genomic features between Ph+ and Ph- groups was done using Fisher exact test and Student’s t-test.

Results:

In total, 34 men were included. Median PSA at MPI detected metastasis was 2.0 ng/mL (range 0.3-20.5), median post-SRT PSA nadir was 0.085 ng/mL (range: 0-5.2), and median PSA doubling time (PSADT) was 5.0 months (range 1.4-14.6). Proportion of OMD patients with PSA <1 ng/mL was 14.7% (n=5) and with PSA<0.5 ng/mL was 3% (n=1). Using Phoenix definition for BCR, 17 patients were Ph+ and 17 Ph-. Mean lesion number detected was higher at 2.41 (SD=1.28) for Ph+ versus 1.47 (SD=0.874) for Ph-. There were no significant differences in T-stage, Grade Group, PSADT, or proportions of mutations in key genes (TP53, SPOP, and DNA damage repair genes) in Ph+ and Ph- groups. On univariable Cox regression, longer PSADT at recurrence was associated with improved PFS (HR=0.837, 95% CI: 0.722-0.972; p=0.019). Ph-status was not associated with PFS. In the Ph+ cohort, p53-mutation may predict for worse PFS (p-interaction=0.017), whereas DNA damage repair gene mutations may predict for better PFS (p-interaction=0.018).

Conclusion:

Molecular PET imaging detects oligorecurrent disease well below PSA levels meeting the Phoenix criteria for BCR. More lesions are detected at higher PSAs. Higher PSA at detection alone may not predict clinical trajectory, which may depend on factors such as PSADT and specific gene mutations.