The Added Value of Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography to Magnetic Resonance Imaging for Local Staging of Prostate Cancer in Patients Undergoing Radical Prostatectomy

BACKGROUND AND OBJECTIVE: The role of prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET)/computed tomography (CT) in addition to magnetic resonance imaging (MRI) for local staging of prostate cancer (PC) has been poorly addressed so far. Our aim was to assess the diagnostic accuracy of PSMA PET/CT and MRI, alone and combined, for detection of extraprostatic extension (EPE) and seminal vesicle invasion (SVI) in PC. METHODS: We conducted a multicenter retrospective study evaluating patients undergoing PSMA PET/CT and MRI before radical prostatectomy. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the receiver operating characteristic curve (AUC) for detection of EPE and SVI were calculated for MRI and PSMA PET/CT alone and combined. KEY FINDINGS AND LIMITATIONS: We included 550 patients, of whom 2%, had low-risk, 43% had intermediate-risk, and 55% had high-risk PC. Overall, 52% of patients had EPE and 21% had SVI at histopathology. Patient-based comparison of MRI versus PSMA PET/CT for detection of EPE revealed sensitivity of 60% versus 41% (p < 0.001), specificity of 77% versus 83% (p = 0.075), PPV of 75% versus 73% (p = 0.6), NPV of 64% versus 56% (p < 0.001), and AUC of 69% versus 62% (p = 0.01). Combining the modalities increased the sensitivity (73%; p < 0.001) and NPV (69%; p < 0.001) and decreased the specificity (67%; p < 0.001) and PPV (71%; p = 0.01) over MRI alone. Patient-based comparison of MRI versus PSMA PET/CT for detection of SVI revealed sensitivity of 36% versus 44% (p = 0.2), specificity of 96% versus 96% (p > 0.99), PPV of 71% versus 75% (p = 0.6), NPV of 85% versus 87% (p = 0.2), and AUC of 66% versus 70% (p = 0.2). Combining the modalities increased the sensitivity (60%; p < 0.001), NPV (90%; p < 0.001), and AUC (76%; p < 0.001) and decreased the specificity (92%; p < 0.001) over MRI alone. Limitations include the retrospective nature of the study, selection of higher-risk cases for PSMA PET/CT, and lack of central review. CONCLUSIONS AND CLINICAL IMPLICATIONS: PSMA PET/CT has lower sensitivity for EPE detection in comparison to MRI. However, addition of PSMA PET information to MRI improved the sensitivity for EPE and SVI detection. Thus, the two modalities should be combined to guide treatment selection. PATIENT SUMMARY: Combining MRI (magnetic resonance imaging) scans with another type of imaging called PSMA PET/CT (prostate-specific membrane antigen positron emission tomography/computed tomography) for patients with prostate cancer leads to better identification of cancer growth outside the prostate in comparison to MRI alone. This could potentially improve the choice of prostate cancer treatment.