⁶⁸Ga-PSMA-11 PET/MR Imaging before prostatectomy: correlation with surgical pathology and two-year follow up

Objectives: To examine the diagnostic utility of ⁶⁸Ga PSMA-11 positron emission tomography (PET)/magnetic resonance (MR) imaging in pre-surgical evaluation of newly diagnosed prostate carcinoma for assessment of extent of disease and prognosis.

Methods: Patients with biopsy-proven Gleason score (GS) ≥7 prostate adenocarcinoma underwent imaging prior to radical prostatectomy. All available clinical and pathological data and PSA levels within 2 years after PET/MR was analyzed to determine the extent of disease and short-term prognosis and concordance between imaging findings and clinico-pathological data.

Results: Of 38 consecutively scanned patients, 33 with follow up data were included in the analysis (29 more than 2 years, 2 for less than 1 year). Thirty patients had focal radiotracer uptake in one or both prostate lobes concordant with the involved lobe(s) on pathology. Two patients had diffuse uptake. There was a positive correlation between SUV and either PSA (R² = 0.41) or percent prostate cancer volume (R² = 0.38). The average SUV_max for patients with a GS of 3+4 was 8.4 g/mL (n=14) vs. 17.4 for GS of 4+3 or higher (n=19, p<0.01). In 5/7 patients with false negative (PI-RADS 1-2, n=3) or indeterminate (PI-RADS 3, n=4) multiparametric prostate MR, PET identified focal uptake concordant with involved lobe. In 6 patients, PET correctly identified a 2nd involved lobe that was occult on MR. In only two cases MR identified an involved lobe not seen on PET. Four patients had pathologically confirmed pelvic nodal involvement (pN1), all had pelvic nodal uptake on PET. None of the 3 patients with inguinal nodal uptake on PET had pathologically confirmed disease or biochemical recurrence after surgery during follow up. One of the two patients with pelvic nodal uptake on PET but negative pathology achieved a post-op PSA of 0.02 with biochemical recurrence (>0.2 ng/mL) at 4 months. Three other patients had detectable PSA after radical prostatectomy: one with osseous metastasis at the time of imaging, and the other two had nodal metastasis. Of 27 patients who had no nodal uptake on PET, undetectable PSA after surgery, and at least 24 months follow up, only two had confirmed biochemical recurrence during follow up period (at 21 and 28 months after imaging).

Conclusions: ⁶⁸Ga PSMA-11 PET/MR is overall highly concordant with surgical pathology and provides complementary information to multiparametric MR for assessment of extent of cancer involvement in prostate gland and pelvic nodes. Patients without nodal involvement on PET in our cohort had a low probability of biochemical recurrence in two years after imaging.