Outcomes of Primary Lymph Node Staging of Intermediate and High Risk Prostate Cancer with 68 Ga-PSMA Positron Emission Tomography/Computerized Tomography Compared to Histological Correlation of Pelvic Lymph Node Pathology.

Purpose: The majority of men who undergo pelvic lymph node dissection at radical prostatectomy have benign lymph node histology. The aim of this study was to assess the predictive value of preoperative ⁶⁸ Ga-PSMA (prostate specific membrane antigen) positron emission tomography/computerized tomography to predict histological metastasis on pelvic lymph node dissection performed during radical prostatectomy.
Materials and Methods: We retrospectively reviewed the sensitivity, specificity, and positive and negative predictive values of preoperative staging ⁶⁸ Ga-PSMA positron emission tomography/computerized tomography to identify histological lymph node metastasis in 208 consecutive men who subsequently proceeded with pelvic lymph node dissection at radical prostatectomy.
Results: Median prostate specific antigen was 7.6 μg/l, the lymph node count was 13 and Gleason score was 4 + 5. On a per patient basis only 21 of the 55 men with metastasis on histological examination were identified on ⁶⁸ Ga-PSMA positron emission tomography/computerized tomography for 38.2% sensitivity. Of the 143 men with no lymph node metastasis on ⁶⁸ Ga-PSMA imaging 34 had metastasis on histology for 80.8% negative predictive value. Specificity was 93.5% and positive predictive value was 67.7%. For the 172 histologically identified malignant lymph node metastases the sensitivity per node was 24.4% and specificity was 99.5%.
Conclusions: If negative ⁶⁸ Ga-PSMA positron emission tomography/computerized tomography is used as the basis of not performing pelvic lymph node dissection, 80% of men would avoid unnecessary pelvic lymph node dissection. However, ⁶⁸ Ga-PSMA positron emission tomography/computerized tomography has poor sensitivity per node to detect all histologically positive lymph node metastases. Thus, pelvic lymph node dissection remains the gold standard to stage pelvic lymph nodes despite its known limitations and complications.