Characterization and PI-RADS version 2 assessment of prostate cancers missed by prebiopsy 3-T multiparametric MRI: Correlation with whole-mount thin-section histopathology

Objectives: To determine the clinical and histopathologic characteristics of missed prostate cancers and their Prostate Imaging Reporting and Data System version 2 (PI-RADS v2) score on a pre-biopsy MRI and subsequent MR-ultrasound (US) fusion biopsy. Methods: We analysed 59 prostate cancer patients who underwent a 3-T MRI prior to an MR-US fusion biopsy and subsequent radical prostatectomy. A radiologist initially reviewed these cases to correlate target lesions and pathology-proven lesions. The patients were categorized as detected or missed prostate cancer cases. Three radiologists independently assigned the PI-RADS v2 score for each case. The missed lesions were further categorized as suspicious or invisible by consensus. The clinical characteristics, PI-RADS v2 scores, and histopathologic features were thereby obtained. Results: Thirty seven (62.7%) of the 59 study cases had a detected prostate cancer and 22 (37.3%) as having missed cancer. Seventeen (77.3%) of the 22 missed patients had a clinically significant lesion. The missed cancer cases had a smaller tumour volume, and higher ADC ratio than the detected cancer cases. Fourteen (63.6%) of the missed lesions were not visible on MRI, even though 71.4% of these cancers were clinically significant. Invisible but clinically significant cancers had a tumour volume below 1 cm(3) in 70% of cases. Conclusions: A negative MRI result does not rule out the current PI-RADS v2 definition of a clinically significant prostate cancer as these tumours can be missed if their volume is below 1 cm(3).