mp-MRI Prostate Characterised PIRADS 3 Lesions are Associated with a Low Risk of Clinically Significant Prostate Cancer - A Retrospective Review of 92 Biopsied PIRADS 3 Lesions.

OBJECTIVE To determine whether prostate image reporting and data system (PIRADS) 3 lesions as assessed by a 3T multiparametric magnetic resonance imaging (MRI) represent clinically significant prostate cancer. METHOD A retrospective review was performed on a series of consecutive patients who underwent MRI guided biopsy of the prostate for clinical suspicion of prostate cancer between January 2013 and March 2014. Demographic, clinical, MRI and biopsy data were reviewed and compared. The same 3T MRI without the use of an endo-rectal coil was employed to assess each patient, obtaining high resolution T2 weighted images, diffusion weighted imaging and dynamic contrast enhancement. The MRI data was sent to Dynacad software for analysis. A single experienced radiologist reported all the studies from this series using a modified PIRADS scoring system. Subsequently, all the lesions marked PIRADS 3 or above were targeted with 18G core biopsy using DynaTrim in-gantry MRI guidance system. Needle position targeting the lesion was recorded prior to each biopsy. All core biopsy samples were sent to one of two pathology laboratories where they were processed and reported as per the International Society of Urological Pathology protocols. RESULTS One hundred and eighteen patients comprising a total of 215 lesions were reviewed. Amongst this cohort, 92 PIRADS 3 lesions were identified and biopsied. The mean age of patients in this cohort was 62.6 years. Median prostate specific antigen (PSA) was 6.5 ng/ml and median prostate size was 78.4 ml. Eightysix (93.5%) of biopsied PIRADS 3 lesions were benign and 6 (6.5%) lesions were found to be malignant. Of these 6 malignant lesions, 4 (66%) were Gleason score 6 (3 + 3) and 2 (33%) were Gleason score 7 (3 + 4). Of the 86 non-malignant lesions, 1 (1.2%) represented high-grade prostate intraepithelial neoplasia and 2 (2.4%) represented atypical small acinar proliferation. PIRADS 3 lesions within the peripheral zone were more likely to be associated with malignant disease compared with lesions identified within the transition zone (10.8 vs. 3.8%). Those with malignant disease had a higher median PSA (8.1 vs. 6.4 ng/ml) and higher median PSA density (0.12 vs. 0.08) than those without malignant disease. Those with benign pathology had a higher prevalence of inflammation (31.4 vs. 16.7%). As per Epstein's criteria, 4 (4.3%) of the biopsied lesions represented clinically significant disease. CONCLUSION We have demonstrated in our series, that prostate lesions characterized on a 3T multiparametric MRI examination of the prostate as PIRADS 3, according to the current prevalent scoring systems, are associated with a low likelihood of the presence of clinically significant prostate cancer.