ASCO GU 2021: Head-to-Head Comparison of 68Ga-PSMA-11 PET/CT and mpMRI in the Detection, Intra-Prostatic Localization, and Local Extension of Primary Prostate Cancer: A Single-Center Imaging Study With Histopathology Gold-Standard

(UroToday.com) Current guidelines for initial staging of intermediate- and high-risk prostate cancer recommend the use of cross-sectional imaging and bone scan, whereas the local staging of prostate cancer relies on systematic or targeted biopsies and multiparametric magnetic resonance imaging (mpMRI). However, the role of prostate-specific membrane antigen (PSMA)-targeted PET in the evaluation of intraprostatic cancer foci and T-staging assessment is not well defined. At the 2021 ASCO Genitourinary Cancers Symposium (ASCO GU), Dr. Ida Sonni and colleagues from UCLA presented results of their study comparing the diagnostic performance of PSMA PET/CT, mpMRI and the combination of the two modalities (PSMA PET/CT plus mpMRI) in the detection, intra-prostatic localization, and local extension of primary prostate cancer with histopathology as the gold standard.

For this study, patients with intermediate- or high-risk prostate cancer underwent a PSMA PET/CT scan and mpMRI prior to intended radical prostatectomy. Patient selection was as follows:

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Each imaging modality was interpreted by three blinded independent readers, whereby a majority rule was applied (2:1). A standardized approach was used to assess the presence, location, and size of prostate cancer foci within the prostate, and the analysis was conducted on a lesion- and segment-level. Segment level analysis was as follows:

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Whole mount pathology was interpreted by a genitourinary trained pathologist using the same standardized method as described above. Accuracy in determining the location, extra-capsular extension and seminal vesicle invasion of prostate cancer foci were assessed using receiver operating characteristic analysis. A “raw-stringent” and “neighboring” approach were used to define imaging/pathology correlation for the detection of individual prostate cancer foci.

The final analysis included 74 patients, with a median age of 65 years (IQR 60-69), median PSA of 11.1 (IQR 7.5-21.5), and including 81% of patients that were D’Amico high risk disease. Detection rate was 75%, 79% and 82% using the “raw-stringent” approach, 86%, 83% and 87% using the “neighboring” approach for PSMA PET/CT, mpMRI and PSMA PET/CT plus mpMRI, respectively. Differences in detection rates between PSMA PET/CT, mpMRI and PSMA PET/CT plus mpMRI were not statistically significant. Additionally, the two imaging modalities performed similarly (AUC = 0.70 vs 0.73, p = 0.09; AUC = 0.77 combined) in localizing prostate cancer. The change in AUC between PSMA PET/CT plus mpMRI and the two imaging modalities alone was statistically significant (p < 0.001), but not between PSMA PET/CT and mpMRI (p = 0.093). mpMRI performed better than PSMA PET/CT in the T-staging assessment: extraprostatic extension (AUC = 0.79 vs 0.59, p = 0.002) and seminal vesicle invasion (AUC = 0.84 vs 0.63, p = 0.001):

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Dr. Sonni concluded this presentation with the following summary points:

  • PSMA PET/CT and mpMRI have similar diagnostic accuracy in the detection and intra-prostatic localization of prostate cancer foci while mpMRI performs better in the assessment of extracapsular extension and seminal vesicle invasion
  • The combination of the two imaging modalities improves performance of the two modalities alone, but this does not reach statistically significant levels on a lesion-level and might not justify changes in the current practices for local staging of prostate cancer

Presented by: Ida Sonni, Associate Project Scientist of University of California, Los Angeles, CA (UCLA)

Co-Authors: Ely Felker, Andrew Thomas Lenis, Anthony E Sisk, Shadfar Bahri, Martin S. Auerbach, Wesley R Armstrong, Voraparee Suvannarerg, Teeravut Tubtawee, Tristan Grogan, David Elashoff, Johannes Czernin, Steven Raman, Robert Evan Reiter, Jeremie Calais; UCLA, Los Angeles, CA; UCLA School of Medicine, Los Angeles, CA; University of California Los Angeles Department of Pathology, Los Angeles, CA; Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA; Ahmanson Translational Theranostics Division, University of California, Los Angeles, CA; University of California Los Angeles, Los Angeles, CA; University of California, Los Angeles, CA; David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA; Institute of Urologic Oncology, University of California, Los Angeles, CA

Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, Twitter: @zklaassen_md during the 2021 ASCO Genitourinary Cancers Symposium (ASCO GU), February 11th to 13th, 2021