Correlation of ⁶⁸Ga-RM2 PET with Postsurgery Histopathology Findings in Patients with Newly Diagnosed Intermediate- or High-Risk Prostate Cancer

Abstract

⁶⁸Ga-RM2 targets gastrin-releasing peptide receptors (GRPRs), which are overexpressed in prostate cancer (PC). Here, we compared preoperative ⁶⁸Ga-RM2 PET to postsurgery histopathology in patients with newly diagnosed intermediate- or high-risk PC. Methods: Forty-one men, 64.0 ± 6.7 y old, were prospectively enrolled. PET images were acquired 42–72 min (median ± SD, 52.5 ± 6.5 min) after injection of 118.4–247.9 MBq (median ± SD, 138.0 ± 22.2 MBq) of ⁶⁸Ga-RM2. PET findings were compared with preoperative multiparametric MRI (mpMRI) (n = 36) and ⁶⁸Ga-PSMA11 PET (n = 17) and correlated to postprostatectomy whole-mount histopathology (n = 32) and time to biochemical recurrence. Nine participants decided to undergo radiation therapy after study enrollment. Results: All participants had intermediate- (n = 17) or high-risk (n = 24) PC and were scheduled for prostatectomy. Prostate-specific antigen was 8.8 ± 77.4 (range, 2.5–504) and 7.6 ± 5.3 ng/mL (range, 2.5–28.0 ng/mL) when participants who ultimately underwent radiation treatment were excluded. Preoperative ⁶⁸Ga-RM2 PET identified 70 intraprostatic foci of uptake in 40 of 41 patients. Postprostatectomy histopathology was available in 32 patients in which ⁶⁸Ga-RM2 PET identified 50 of 54 intraprostatic lesions (detection rate = 93%). ⁶⁸Ga-RM2 uptake was recorded in 19 nonenlarged pelvic lymph nodes in 6 patients. Pathology confirmed lymph node metastases in 16 lesions, and follow-up imaging confirmed nodal metastases in 2 lesions. ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET identified 27 and 26 intraprostatic lesions, respectively, and 5 pelvic lymph nodes each in 17 patients. Concordance between ⁶⁸Ga-RM2 and ⁶⁸Ga-PSMA11 PET was found in 18 prostatic lesions in 11 patients and 4 lymph nodes in 2 patients. Noncongruent findings were observed in 6 patients (intraprostatic lesions in 4 patients and nodal lesions in 2 patients). Sensitivity and accuracy rates for ⁶⁸Ga-RM2 and ⁶⁸Ga-PSMA11 (98% and 89% for ⁶⁸Ga-RM2 and 95% and 89% for ⁶⁸Ga-PSMA11) were higher than those for mpMRI (77% and 77%, respectively). Specificity was highest for mpMRI with 75% followed by ⁶⁸Ga-PSMA11 (67%) and ⁶⁸Ga-RM2 (65%). Conclusion: ⁶⁸Ga-RM2 PET accurately detects intermediate- and high-risk primary PC, with a detection rate of 93%. In addition, ⁶⁸Ga-RM2 PET showed significantly higher specificity and accuracy than mpMRI and a performance similar to ⁶⁸Ga-PSMA11 PET. These findings need to be confirmed in larger studies to identify which patients will benefit from one or the other or both radiopharmaceuticals.