Introduction

Multiparametric prostate magnetic resonance imaging (mpMRI) utilizing the PI-RADS classification system attempts to identify clinically-significant [Gleason score (GS) 7 or higher] prostate cancer (PCa), with PI-RADS 1 or 2 typically corresponding to very low risk of clinically-significant PCa. In this study, we analyzed the clinicopathologic characteristics of patients undergoing prostate core biopsy (PBx) with PI-RADS 1 or 2 lesions.

Methods

All patients at a single large academic institution who had at most PI-RAD 1 or 2 lesions on mpMRI between 1/1/15 and 6/30/16 and underwent pre- or post-MRI PBx were retrospectively identified. All cases of clinically-significant PCa were re-reviewed by study pathologists to confirm pathologic findings; clinicopathologic data from all other cases was obtained from pathology reports and electronic medical records.

Results

276 patients with PI-RADS 1 or 2 lesions were identified, of which 98 (35.5%) had either pre- (60) or post-MRI (38) in-house PBx. Six (6.1%) patients showed GS7 PCa (3 pre- and 3 post-MRI), including 2 with GS4+3=7 tumors. For the remaining patients, the most recent PBx findings included: GS6 PCa (22 pre- and 13 post-MRI); atypical glands (3 pre- and 2 post-MRI); high-grade prostatic intraepithelial neoplasia (5 pre- and 4 post-MRI); or, benign (27 pre- and 16 post-MRI). For patients with GS7 PCa, the median number of involved cores was 1 (range = 1-3), the median number of total cores was 20 (range = 12-30), the median % involvement of a single core was 12.5 (range = 5-25), and the median % Gleason pattern 4 was 30 (range = 5-90); types of Gleason pattern 4 included: poorly-formed glands only (4), cribriform glands only (1), or poorly-formed and cribriform glands (1). One GS7 tumor occurred in the post-radiation (XRT) setting, and one showed aberrant p63 expression; follow-up for patients with GS7 PCa included primary XRT (1), salvage XRT (1), and active surveillance (AS; 4). Nearly all patients (>90%) with GS6 PCa opted for AS; one patient underwent radical prostatectomy (pT2a GS6 PCa), and one patient was lost to follow-up.

Conclusions

The majority (58.2%) of patients with PI-RADS 1 or 2 lesions by mpMRI do not have detectable PCa on core biopsy, however, a small subset (6.1%) harbor GS7 PCa. Although long-term follow-up data are needed, PCa patients with PI-RADS 1 or 2 lesions by mpMRI appear to represent a very low-risk cohort that may be amenable to AS in the majority of cases.

Funding

None