MP67-17 MRI–ULTRASOUND FUSION TARGETED PROSTATE BIOPSY: THE IMPORTANCE OF BIOPSYING OUTSIDE THE MRI LESION

INTRODUCTION AND OBJECTIVES: Suspicious lesions identified on multi-parametric MRI (mpMRI) may be targeted with a growing range of MRI-guided prostate biopsy techniques. It has been suggested that mpMRI could reduce the burden of prostate biopsy by limiting biopsy samples to only the areas suspicious on MRI. This study assessed the performance of mpMRI at excluding clinically significant prostate cancer outside the suspicious MRI lesion. METHODS: A paired cohort study of 104 suspicious lesions identified onmultiparametric MRI. Lesions weremarked with an arrow by an expert uro-radiologist and scored from 1 to 5 according to the European Consensus guidelines (PI-RADS). MRI-US fusion targeted biopsy of the lesion was performed using Varian brachytherapy software (Variseed 8.0.2, Varian Medical Systems). After targeting the lesion, the remaining prostate was systematically sampled with transperineal sector biopsy (min 24 max 38 cores). This technique preferentially targets the peripheral zone by sectors and any prostate cancer identified outside the lesion was located into a prostate quadrant. RESULTS: Outside the MRI lesion, clinically significant prostate cancer was identified in 39% (41/104) and there was upgrading of the Gleason score in 16% (17/104). This MRI invisible cancer was located in the same quadrant of the lesion in 9%, in an adjoining quadrant in 22% and in non-adjoining quadrant in 9%. The cancer detection rate within theMRI lesionwas 57% (60/104). As the PI-RADS score increased, the detection rate of clinically significant cancer increased (p<0.001, chi squared test). The cancer detection rate for PI-RADS 3 was 31%, PI-RADS 4 was 64% and PI-RADS 5 was 82%. Overall, when MRI-guided biopsy was combined with transperineal sector biopsy the cancer detection rate was 68% (70/104). CONCLUSIONS: MRI-guided prostate biopsies provide good detection rates particularly in PI-RADS 4 and 5 lesions. However, there is ‘MRI Invisible’ cancer which will be missed if biopsies are limited to the lesion only. The highest cancer detection rate was achieved by combining MRI-guided biopsy with transperineal biopsy to assess the rest of the prostate. MRI-targeted biopsy techniques should incorporate a systematic biopsy protocol to identify all clinical significant disease. The presence of ‘MRI Invisible’ cancer also has implications for the planning of focal or targeted therapies.