PD27-01: Predicting Extra-prostatic Extension (EPE) for surgical guidance in prostate cancer: A comparison of biopsy pathology, multiparametric MRI, and PSMA-PET

Clinton Bahler*, Mark Green, Mark Tann, Katrina Collins, Jordan Swensson, Eric Brocken, Liang Cheng, Carla Mathias, Indianapolis, IN, David Alexoff, Hank Kung, Philadelphia, PA, Gary Hutchins, Michael Koch, Indianapolis, IN

Introduction: Prostatectomy related incontinence and impotency result from injury to nerves and muscle tissue.  Preserving nerves and muscle adjacent to the prostate risks positive margins; therefore, preoperative imaging is needed with high sensitivity for extra-prostatic extension.

Methods: Four clinical trials for PSMA-PET targeted imaging prior to prostatectomy were retrospectively evaluated for prediction of extra-prostatic extension as documented on post-surgical whole-mount pathologic analysis. Two different PSMA-PET tracers were included: PSMA-11 and P16-093. A blinded review of PET and MRI scans was performed to predict the risk of extra-prostatic extension (EPE). Stata 13.1 was used. Pearson’s Chi2 and McNemar’s Chi2 were used for accuracy statistics.

Results: Pre-operative PSMA-PET imaging was performed in 71 patients with either 68Ga-P16-093 (n=25) or 68Ga-PSMA-11 (n=46).  Age (62 vs 61 years), PSA (7.3 vs 7.8), and biopsy pathology (3+3: 0 vs 7%, 3+4: 28 vs 39%, 4+3: 24 vs 20%, =4+5: 48 vs 35%) were similar between the groups (p>0.30).  There were 24 (34%) with pT3a (EPE) and 16 (23%) with pT3b on final pathology.  Overall positive margin rate was 17 (24%).  Index lesion SUVmax was similar between P16-093 and PSMA-11 (10.3 vs 11.7).  EPE Sensitivity (87 vs 92%), Specificity (77 vs 76%), and ROC area (82 vs 84%) were similar between P16-093 and PSMA-11, respectively (p=0.87).  MRI (available in 45) found high specificity (83%) but low sensitivity (60%) and the overall ROC area was lower when compared to pooled PSMA-PET (0.72 vs 0.83, p=0.01).  For pooled PSMA-PET imaging, a treatment change from “non-nerve sparing” to “nerve sparing” was recommended in 21/71 (30%) of patients.  A total of 14 men had nerve-sparing (treatment change) based on PSMA-PET imaging with one (5%) having a positive margin.  Figure 1 shows a case where left-sided EPE as accurately predicted by 68Ga-P16-093 scan.

Conclusions: PSMA-PET imaging can improve surgical guidance in men with =4+3 prostate cancer resulting in preservation of nerve-bundles. 68Ga-P16-093 PET and 68Ga-PSMA-11 PET had similar accuracy for predicting extra-prostatic extension.

Source of Funding: Al Christy Prostate Cancer Fund, R44 CA233140, NIH Small Business Innovation Research grant (SBIR), CTSI NIH/NCRR Grant Number UL1TR001108, ACS-IRG Grant Mechanism (16-192-31)