Introduction

Multiparametric Prostate Magnetic Resonance Imaging (mpMRI) utilizes a PI-RADS classification system to identify clinically significant (Gleason score (GS) 7 or higher) prostate adenocarcinoma (PCa) with PI-RADS 5 lesions typically corresponding to a high-risk of clinically significant PCa.

Methods

All patients who underwent mpMRI between 1/1/2015 and 6/30/2016 at a large academic institution were identified. Patients with one or more PI-RADS 5 lesions who underwent an ultrasound-MRI fusion PBx were retrospectively reviewed to assess for presence or absence of PCa, location (targeted vs. 12-core/non-targeted cores), GS, and percentage pattern 4 in GS 7 tumors.

Results

138 patients with PI-RADS 5 lesions {1 lesion (107), 2 lesions (27), 3 lesions (4)} were identified, of which 76 (55%) underwent an in-house MRI fusion PBx. In the targeted cores, 7 (9%) patients had no PCa and 69 (91%) patients showed PCa. In 7 patients without PCa (total 12 PI-RADS 5 lesions), the targeted cores showed extensive simple atrophy (2), florid adenosis (1), central zone histology (2), atypical small acinar proliferation (1), focal high-grade prostatic intraepithelial neoplasia (1), granulomatous inflammation (1), carcinoid (1), focal simple atrophy (2) and focal adenosis (1). Clinically significant PCa was noted in 79% (60/76) cases, {GS 3+4 (35), GS 4+3 (16) and GS 8-10 (9)}. In 7 (9%) patients with GS 7 or higher PCa, the highest GS was found in the non-targeted cores. The median % Gleason pattern 4 in GS 7 tumors was 30 (inter-quartile range = 10-60). Of the remaining 62 (45%) patients who did not receive an MRI fusion PBx, 3 had saturation PBx and 27 had a radical prostatectomy (all show GS 7 or higher PCa); 9 received radiation and/or hormone therapy.

Conclusions

The vast majority of patients (79%) with PI-RADS 5 lesions showed GS 7 or higher PCa on targeted cores; however, a small subset (9%) showed no evidence of malignancy. The benign mimickers of PI-RADS 5 lesions include florid adenosis (1), granulomatous inflammation (1), carcinoid (1), central zone acini (2) and simple atrophy (2). PI-RADS 5 lesions can be biopsied for confirmation of clinically significant disease in the vast majority of cases or used to guide the patient's treatment towards more definitive therapies.

Funding

None