68 Ga-PSMA PET/CT and mpMRI for primary lymph node staging of intermediate to high-risk prostate cancer: a systematic review and meta-analysis of diagnostic test accuracy

Purpose To evaluate the diagnostic accuracy of Gallium-68 prostate-specific membrane antigen positron emission tomography-computed tomography ( 68 Ga-PSMA PET/CT) compared with multiparametric magnetic resonance imaging (mpMRI) for detection of metastatic lymph nodes in intermediate to high-risk prostate cancer (PCa). Methods PRISMA-compliant systematic review updated to September 2020 was performed to identify studies that evaluated the diagnostic performance of 68 Ga-PSMA PET/CT and mpMRI for detection of metastatic lymph nodes in the same cohort of PCa patients using histopathologic examination as a reference standard. The quality of each study was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) instrument. STATA version 16.0 was used to obtain the pooled estimates of diagnostic accuracy for per-patient and per-lesion analyses. Heterogeneity in the accuracy estimates was explored by reviewing the generated forest plots, summary receiver operator characteristic (SROC) curves, hierarchical SROC plots, chi-squared test, heterogeneity index, and Spearman’s correlation coefficients. Results Six studies, which included 476 patients, met the eligibility criteria for per-patient analysis and four of these studies, reporting data from 4859 dissected lymph nodes, were included in the per-lesion analysis. In the per-patient analysis ( N = 6), the pooled sensitivity and specificity for 68 Ga-PSMA PET/CT were 0.69 and 0.93, and for mpMRI the pooled sensitivity and specificity were 0.37 and 0.95. In the per-lesion analysis ( N = 4), the pooled sensitivity and specificity for 68 Ga-PSMA PET/CT were 0.58 and 0.99, and for mpMRI the pooled sensitivity and specificity were 0.44 and 0.99. There was high heterogeneity and a threshold effect in outcomes. A sensitivity analysis demonstrated that the pooled estimates were stable when excluding studies with patient selection concerns, whereas the variances of the pooled estimates became significant, and the characteristics of heterogeneity changed when excluding studies with concerns about index imaging tests. Conclusion Both imaging techniques have high specificity for the detection of nodal metastases of PCa. 68 Ga-PSMA PET/CT has the advantage of being more sensitive and making it possible to detect distant metastases during the same examination. These modalities may play a complementary role in the diagnosis of PCa. Given the paucity of data and methodological limitations of the included studies, large scale trials are necessary to confirm their clinical values.