Association of Anterior and Lateral Extraprostatic Extensions with Base-Positive Resection Margins in Prostate Cancer

INTRODUCTION Positive surgical margins (PSM) detected in the radical prostatectomy specimen increase the risk of biochemical recurrence (BCR). Still, with formidable number of patients never experiencing BCR in their life, the reason for this inconsistency has been attributed to the artifacts and to the spontaneous regression of micrometastatic site. To investigate the origin of margin positive cancers, we have looked into the influence of extraprostatic extension location on the resection margin positive site and its implications on BCR risk. MATERIALS & METHODS The clinical information and follow-up data of 612 patients who had extraprostatic extension and positive surgical margin at the time of robot assisted radical prostatectomy (RARP) in the single center between 2005 and 2014 were modeled using Fine and Gray's competing risk regression analysis for BCR. Extraprostatic extensions were divided into categories according to location as apex, base, anterior, posterior, lateral, and posterolateral. Extraprostatic extensions were defined as presence of tumor beyond the borders of the gland in the posterior and posterolateral regions. Tumor admixed with periprostatic fat was additionally considered as having extraprostatic extension if capsule was vague in the anterior, apex, and base regions. Positive surgical margins were defined as the presence of tumor cells at the inked margin on the inspection under microscopy. Association of these classifications with the site of PSM was evaluated by Cohen's Kappa analysis for concordance and logistic regression for the odds of apical and base PSMs. RESULTS Median follow-up duration was 36.5 months (interquartile range[IQR] 20.1-36.5). Apex involvement was found in 158 (25.8%) patients and base in 110 (18.0%) patients. PSMs generally were found to be associated with increased risk of BCR regardless of location, with BCR risk highest for base PSM (HR 1.94, 95% CI 1.40-2.68, p<0.001) after adjusting for age, initial prostate-specific antigen, pathologic Gleason score, and pathologic T stage in the multivariate model. Logistic regression for PSM site revealed no significant correlation of apex PSM with extraprostatic extension location, while base PSM was associated with increased odds of anterior (OR 2.513, 95% CI 1.425-4.430, p = 0.001) and lateral (OR 2.715, 95% CI 1.735-4.250, p<0.001) extraprostatic extension. CONCLUSION Extension into the extraprostatic tissue on some specific locations do not share the same recur risk due to the different anatomical structures surrounding the organ. Anterior and lateral EPEs are prone to leave PSM on the base of the prostate, probably because of the lack of anatomical barricades slowing down the direct invasion process. More study on the pattern of spread of the tumors found to have extraprostatic extension is suggested for optimal planning of the operation extent and of the adjuvant radiotherapy.