Performance and inter-observer variability of prostate MRI (PI-RADS version 2) outside high-volume centres

Objective: Despite the growing trend to embrace pre-biopsy MRI in the diagnostic pathway for prostate cancer (PC), its performance and inter-observer variability outside high-volume centres remains unknown. This study aims to evaluate sensitivity of and variability between readers of prostate MRI outside specialized units with radical prostatectomy (RP) specimen as the reference standard. Materials and methods: Retrospective study comprising a consecutive cohort of all 97 men who underwent MRI and subsequent RP between January 2012 and December 2014 at a private hospital in Sweden. Three readers, blinded to clinical data, reviewed all images (including 11 extra prostate MRI to reduce bias). A tumour was considered detected if the overall PI-RADS v2 score was 3-5 and there was an approximate match (same or neighbouring sector) of tumour sector according to a 24 sector system used for both MRI and whole mount sections. Results: Detection rate for the index tumour ranged from 67 to 76%, if PI-RADS 3-5 lesions were considered positive and 54-66% if only PI-RADS score 4-5 tumours were included. Detection rate for aggressive tumours (GS >= 4+3) was higher; 83.1% for PI-RADS 3-5 and 79.2% for PI-RADS 4-5. The agreement between readers showed average j values of 0.41 for PI-RADS score 3-5 and 0.51 for PI-RADS score 4-5. Conclusions: Prostate MRI evidenced a moderate detection rate for clinically significant PC with a rather large variability between readers. Clinics outside specialized units must have knowledge of their performance of prostate MRI before considering omitting biopsies in men with negative MRI.