Comparison of 68Ga-PSMA-11 PET/CT and mpMRI, Alone and In Combination in Primary Prostate Cancer

THE DIAGNOSTIC PERFORMANCE of prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET)/computed tomography (CT), multi-parametric magnetic resonance imaging (mpMRI), and PSMA PET/CT plus mpMRI in primary prostate cancer was similar in the detection and intra-prostatic localization of prostate cancer foci, according to a study presented at the 2021 ASCO Genitourinary Cancers Symposium. mpMRI was superior in assessing extra-capsular extension (ECE) and seminal vesicle invasion (SVI), explained Dr. Ida Sonni (UCLA, Los Angeles) during a session on “Practical applications of novel imaging and genomics approaches in the management of clinically localized prostate cancer.”

Current guidelines recommend the use of cross-sectional imaging, such as CT and MRI, as well as bone scans for the initial staging of intermediate- and high-risk prostate cancer. Specifically, the local staging relies on systematic or targeted biopsies, as well as multiple-parametric MRI, but both of them have limitations. “Since the introduction of PSMA PET less than one decade ago, the approach to imaging of prostate cancer has been rapidly changing, Dr. Sonni explained.

“So we had one main question in mind when we initiated this study: What is the role of PSMA PET/CT in the local T staging of prostate cancer?” she said.

The study enrolled patients with intermediate- or high-risk prostate cancer who underwent a PSMA PET/CT scan and mpMRI ahead of intended radical prostatectomy. Three blinded, independent nuclear medicine physicians interpreted the PSMA PET/CT scans, and three radiologists reviewed the mpMRI results. The presence, location, and size of prostate cancer foci were evaluated using a standardized approach. A genitourinary pathologist interpreted whole mount pathology. Receiver operating characteristic (ROC) analysis was implemented to evaluate accuracy in determining the location, extra-capsular extension (ECE), and seminal vesicle invasion (SVI) of prostate cancer foci. “Raw-stringent” and “neighboring” approaches were implemented to define imaging/pathology correlation to detect individual prostate cancer foci.

Seventy-four patients were included in the final analysis. Per the “raw stringent” approach, the detection rates were: PSMA PET/CT, 75%; mpMRI, 79%; and PSMA PET/CT plus mpMRI, 82%. Per the “neighboring” approach, the detection rates were 86%, 83%, and 87%, respectively. Differences in detection rates among PSMA PET/CT, mpMRI, and PSMA PET/CT plus mpMRI did not reach statistical significance. In localizing prostate cancer, the area under the ROC (AUC) for PSMA PET/ CT was 0.70 compared with 0.73 for mpMRI (P=0.09), and for the two modalities together, the AUC was 0.77. In the T-staging assessment, mpMRI was superior to PSMA PET/CT (ECE: AUC, 0.79 vs. 0.59; P=0.002; SVI: AUC, 0.84 vs. 0.63; P=0.001).

“PSMA PET CT and multiparametric MRI have complementary roles in the local T staging of intermediate- and high-risk prostate cancer,” Dr. Sonni concluded.

Dr. Sonni and co-investigators concluded that although the combination of the two imaging modalities improved the performance of the two modalities alone, since the difference was not statistically significant on a lesion-level, it might not justify changing current practices for local staging of prostate cancer.

Reference:

Sonni I, Felker E, Lenis AT, et al. 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. J Clin Oncol. 2021;39(6, suppl):49. Abstract 193. doi: 10.1200/JCO.2021.39.6_suppl.193