To provide insights into the role of mpMRI for predicting oncological control following two focal ablation (FA) templates for selective cases of prostate cancer (PCa).

59 radical prostatectomies were performed between 2012 and 2016 on cases that fulfilled criteria for FA. The Gleason score (GS), extent of Gleason pattern (GP) 4, maximum linear cross sectional length (MLCSL) and location of tumor foci were recorded and related to scale on corresponding 3mm transverse slice prostate maps. Gleason pattern 4 extra-focal disease (GP4EFD) was defined as PCa with any GP 4 not detected by mpMRI and transrectal ultrasound systematic biopsy observed outside a specified ablation zone. The location of these GP4EFD relative to the MRI lesion (MRI-L) (contralateral or ipsilateral) was recorded and used to predict oncological control following a hypothetical margin and ipsilateral hemi-ablation templates.

Overall, 15/59 (25.4%) of the prostate specimens had at least one GP4EFD. Of the total 20 GP4EFD, 7/20 (35%) were ipsilateral and 13/20 (65%) were contralateral to the MRI-L. Of the GP4EFD, 16/20 (80%), 2/20 (10%), and 2/20 (10%) were GS 3+4, GS 4+3, and GS 4+4, respectively. Of these GP4EFD, 10/20 (50%) exhibited a MLCSL < 5mm. Ablating only the MRI-L+10mm or performing a ipsilateral hemi-ablation would leave residual GP4 in 14/59 (23.7%) and 11/59 (18.6%) of cases, respectively.

Since a significant proportion of candidates for FA based on mpMRI and systematic biopsy will have pre-existing GP4EFD outside ablation templates, active surveillance of the untreated prostate is mandatory.