3259 - Preliminary Results of a Prospective Study Investigating the Relationship between Change in PET Signal and Changes in Pathology Pre- to Mid-Treatment In High Risk Prostate Cancer
Presenter(s)
D. Duenas1, W. Huang2, J. A. Benson2, J. Slagowski3, R. Hutten1, D. Jarrard4, S. G. Zhao5, S. Y. Cho6, and J. M. Floberg3; 1Department of Human Oncology, University of Wisconsin Hospitals and Clinics, Madison, WI, 2University of Wisconsin School of Medicine and Public Health, Madison, WI, 3Department of Human Oncology, University of Wisconsin-Madison, Madison, WI, 4Department of Urology, University of Wisconsin Hospitals and Clinics, Madison, WI, 5University of Wisconsin, Madison, WI, 6Department of Radiology, University of Wisconsin Schools of Medicine and Public Health, Madison, WI
Purpose/Objective(s): The association between change in prostate specific membrane antigen positron emission tomography (PSMA PET) signal and treatment response is not established, nor is the biological significance of pre- or mid-treatment PSMA PET signal well understood. We report preliminary results from a pilot study investigating change in PSMA PET signal pre- to mid-treatment and pathologic response in men with high-risk prostate cancer treated with external beam radiation therapy (EBRT), high dose-rate (HDR) prostate brachytherapy, and androgen deprivation therapy (ADT). We also evaluated associations between PSMA PET signal and PAM50 and PORTOS classifications to explore relationships with imaging and pathologic response.
Materials/Methods: In this IRB-approved pilot trial, we obtained mid-treatment PSMA PET/MRI and biopsies in men undergoing EBRT, HDR brachytherapy and ADT. Patients received neoadjuvant, concurrent and adjuvant ADT (total 6-24 months). Pre-treatment biopsies were analyzed with a genomic classifier to derive PAM50 and PORTOS scores. Mid-treatment PSMA PET/MRI was obtained between EBRT and brachytherapy. Mid-treatment transperineal prostate fusion biopsies were obtained during brachytherapy, targeting lesions of interest (LOIs) identified on staging imaging and pre-treatment biopsies. Pre- and mid-treatment PET scans were registered and LOIs contoured to measure maximum standardized uptake value (SUVmax). Subjective PET response was assessed. The epithelial-stromal ratio (E/S) of pre-and mid-treatment prostate biopsies assessed partial pathologic response. Changes in SUVmax and E/S were evaluated using the Wilcoxon signed rank test. Associations between SUVmax and genomic classifiers, and changes in SUVmax and these classifiers, were assessed using the Kruskal-Wallis and Wilcoxon rank-sum tests.
Results: Imaging and pre-treatment genomic data were analyzed from 17 patients. All had at least a partial response on PSMA PET; 7/17 had a complete response. Mean SUVmax decreased significantly pre- to mid-treatment (19.0 vs. 5.38, p<0.00001). There was likewise a significant decrease in the E/S pre- to mid-treatment (p=0.002). There was no significant difference in baseline PSMA SUVmax between PAM50 groups (p = 0.88) or PORTOS classification (p=1.0). Pre-and mid-treatment pathology analysis was completed for the initial 6 patients. There was likewise no difference in change of PSMA PET SUVmax pre- to mid-treatment between PAM50 group or PORTOS classification (p=0.74, p=0.80, respectively).
Conclusion: In this preliminary report, all patients undergoing EBRT, brachytherapy, and ADT showed a significant reduction in PSMA SUVmax pre- to mid-treatment, and there was likewise a reduction in the E/S, indicating a partial pathologic response. These findings support the feasibility of relating changes in PSMA PET signal to pathologic response.