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JU INSIGHT Comparing MRI and PSMA-PET for Predicting Extraprostatic Extension of Prostate Cancer and Surgical Guidance

By: Clinton D. Bahler, MD*, Indiana University, Indianapolis; Isamu Tachibana, MD*, Indiana University, Indianapolis; Mark Tann, MD, Indiana University, Indianapolis; Katrina Collins, MD, Indiana University, Indianapolis; Jordan K. Swensson, MD, Indiana University, Indianapolis; Mark A. Green, PhD, Indiana University, Indianapolis; Carla J. Mathias, BA, Indiana University, Indianapolis; Yan Tong, PhD, MS, Indiana University, Indianapolis; Courtney Yong, MD, Indiana University, Indianapolis; Ronald S. Boris, MD, Indiana University, Indianapolis; Eric Brocken, MS, Indiana University, Indianapolis; Gary D. Hutchins, PhD, Indiana University, Indianapolis; Justin B. Sims, MD, Indiana University, Indianapolis; Danielle V. Hill, MD, Indiana University, Indianapolis; Nathaniel Smith, PhD, Indiana University, Indianapolis; Christopher Ferari, MD, Indiana University, Indianapolis; Harrison Love, MD, Indiana University, Indianapolis; Michael O. Koch, MD, Indiana University, Indianapolis; *Co-first authors | Posted on: 14 Aug 2024

Bahler CD, Tachibana I, Tann M, et al. Comparing magnetic reson ance imaging and prostate- specific membrane antigen– positron emis sion tomography for prediction of extraprostatic extension of prostate cancer and surgical guidance: a prospective nonrandomized clinical trial. J Urol. 2024;212(2):290-298. doi:10.1097/JU.0000000000004032

Study Need and Importance

Advanced prostate imaging with MRI has greatly increased personalized medicine by shifting to a lesion-based approach. This lesion-based approach has enabled targeted biopsy and refinement of surgical plans for both focal therapy and radical prostatectomy. For radical prostatectomy, predicting extraprostatic extension (EPE) is critical to safely select men for nerve-sparing surgery and continence-sparing approaches such as Retzius sparing. However, enthusiasm for MRI has been tempered with real-world sensitivity for EPE near 60%. Prostate cancer is difficult to image with anatomy-based modalities (ultrasound, CT, MRI, etc). 68Ga–prostate-specific membrane antigen–11 positron emission tomography CT (PSMA-PET) offers the advantage of molecularly targeted tracers with high sensitivity for lesions likely to have EPE (Gleason ≥4+3). We hypothesized that PSMA-PET, when compared to MRI, would have increased sensitivity for EPE.

What We Found

Fifty patients were prospectively enrolled, and the population was weighted toward EPE (44%) and high-risk with Gleason grade 3 + 4 (30%), 4 + 3 (30%), and 4 + 4/4 + 5 (38%). Radiologists knew patients were scheduling for prostatectomy, but they reviewed anonymized images with no clinicopathologic information (blinded). The sensitivity was higher for PSMA-PET when compared to MRI (86% vs 57%, P = .03), while specificity was similar. The PSMA-PET changed the surgical plan from nonnerve sparing to nerve sparing in 20 (40%) cases and from nerve sparing to nonnerve sparing in 5 cases. The Figure demonstrates the ability of PSMA-PET to locate tumors near the prostate capsule at risk for EPE. The positive margin rate was not increased in patients with treatment change toward nerve-sparing.

Image

Figure. This patient had PSA of 4.9, prostate size 48 cm 3 (PSA density: 0.10), and Gleason biopsy worst core of 4 + 4. His final pathology showed Gleason 3 + 4 and pT3a. Gleason patterns 3 and 4 are listed by lesion. The MRI did not predict extraprostatic extension (EPE), while the 68 Ga–prostate-specific membrane antigen–11 positron emission tomography CT (PET) interpretation showed possible bilateral EPE. Final pathology showed left-sided EPE. NVB indicates neurovascular bundle.

Limitations

This is a single-institution study with expert radiology interpretations. Imaging accuracy could vary based on the quality of PET scanner and experience of the radiologists.

Interpretation for Patient Care

In this prospective trial, PSMA-PET resulted in higher sensitivity for EPE and increased the nerve-sparing rate during radical robotic prostatectomy without increasing positive margins.

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