MP18-09 WHEN IS TUMOUR VOLUME AN EXCLUSION CRITERIA FOR FOCAL THERAPY? RESULTS FROM A RADICAL PROSTATECTOMY SERIES

INTRODUCTION AND OBJECTIVES: When focal therapy (FT) is performed with sufficient intensity to eradicate cancer, accurate evaluation for the extent of significant cancer (SC) is essential to avoid undertreatment. By D0Amico risk category of prostate cancer (PC), we assessed the possibility of underdiagnosis by MRI and biopsy for: 1) extra-prostatic extension (EPE) at the ablation field; and 2) SC left in untreated area. We then verified the applicability of quadrant-based regional FT to intermediateand high-risk PC, compared with lowrisk PC. METHODS: We enrolled 203 PC patients in clinical stage T 2 on digital rectal examination who underwent multiparametric MRI, systematic 14-core biopsy, and radical prostatectomy. MRI interpretation followed the Prostate Imaging Reporting and Data System version 2. Cancer distribution was analyzed using a quadrant basis. Anterior and posterior prostatic quadrants were assessed through 4 anterior/lateral cores and 4 posterior/lateral cores, respectively. Additional MRI-targeted sampling was included in the assessment of Gleason score (GS). SC was defined as a lesion with volume 0.5 mL and/or GS 4+3 and/or EPE. We consider that the absence of EPE is a precondition for FT and that the absence of SC is prerequisite for the untreated area. Each prostate was examined for EPE using MRI, and each quadrant was then assessed for SC using MRI and 4 biopsy cores. RESULTS: In total, 35/109/59 men were classified as low-/ intermediate-/high-risk cases, respectively. In each risk groups, radiological EPE (rEPE) features on MRI were absent in 31/49/21 men (89/45/36% of each group). Among men without rEPE features in each group, EPE was pathologically absent in 30/47/19 men (97/96/90%) (p 1⁄4 1.00 and 0.56 in intermediateand high-risk groups, respectively, vs. the low-risk group). In men without rEPE features, SC was absent in 44/55/23 anterior quadrants (71/56/55%) and 46/55/22 posterior quadrants (74/56/52%). Negative predictive values of the combination of MRI and biopsy for SC were 95/96/100% in anterior quadrants (p 1⁄4 1.00 and 1.00 in intermediateand high-risk groups, respectively, vs. the low-risk group) and 94/98/89% in posterior quadrants (p 1⁄4 0.58 and 0.61). CONCLUSIONS: In intermediateand high-risk PC selected through MRI and biopsy, EPE is absent in 96% and 90% of men, respectively, and SC left in the untreated area is absent in 96-98% and 89-100% of quadrants, respectively, which suggests that FT is an option for intermediate-risk PC as well as low-risk PC. Although carefullyselected high-risk PC might also be a candidate for FT, further study using a larger cohort is needed.