Comparison of 68Ga-PSMA PET/CT and mp-MRI in regard to local staging for prostate cancer with histopathological results: A retrospective study.

Background: Imaging modalities are used to diagnose and clinical grading of clinically significant prostate cancer. In this study, 68Ga-PSMA PET/CT (PSMA) and multiparametric prostate MRI (mp-MRI) were compared in regard to locating intraprostatic tumor and locoregional staging.

Methods: After ethics committee approval, a total of 49 patients with prostate cancer who had mp-MRI and PSMA before radical prostatectomy were included. Preoperative and postoperative PSA, transrectal ultrasound-guided prostate biopsy (TRUS-Bx) ISUP grade, radical prostatectomy ISUP grade, body mass index (BMI), TRUS prostate volume, mp-MRI tumor mapping, PSMAtumor mapping, pathologic tumor mapping, extraprostatic extension (EPE), seminal vesicle invasion (SVI), lymph node invasion (LNI), and bladder neck invasion (BNI)were retrospectively evaluated. Index tumor was located by uroradiologist, nuclear medicine specialist, and uropathologist on a 12-sector prostate pathology map and compared with each other in terms of accuracy and locoregional clinical staging.

Results: Mean age of the patients was 66.18 ± 6.67 years and the mean of preoperative PSA results was 21.11 ± 32.56 ng/ml. Nearly half of the patients' (44.9%) pathology was reported as ISUP grade 4 and 5% and 18.4% of patients were surgical margin positive. According to the pathological findings, 362 out of 588 sectors were tumor-positive, 174 out of 362 sectors were tumor-positive in mp-MRI, and 175 out of 362 sectors were tumor-positive in PSMA. Both PSMA and mp-MRI were comparable (p = 0.823) and accurate to detect the location of the intraprostatic index tumor (AUC = 0.66 vs. 0.69 respectively, p = 0.82). The sensitivity and the specificity of the PSMA and mp-MRI for localizing intraprostatic index tumors were 42.5% versus 49.5% and 90.7% versus 88.6% respectively. mp-MRI was more accurate than PSMA in terms of EPE (AUC = 0.8 vs. AUC = 0.57 respectively, p = 0.027) and both methods were comparable in terms of SVI (AUC = 0.75 vs. AUC = 0.75, p = 0.886) and BNI (AUC = 0.51 vs. AUC = 0.59, p = 0.597). PSMA and mp-MRI were comparable in terms of LNI (AUC = 0.76 vs. AUC = 0.64, p = 0.39).

Conclusion: mp-MRI should be considered for its high accuracy in the diagnosis of EPE, especially before decision-making for nerve-sparing surgery in high-risk patients. Both imaging modalities were accurate for localizing intraprostatic index tumor. PSMA is accurate for detecting LNI.