Quantitative perineural invasion is a prognostic marker in prostate cancer

This study aimed to investigate the prognostic value of a quantitative, detailed, yet practical analysis of perineural invasion in radical prostatectomy specimens in a high-risk prostate cancer cohort. A total of 114 patients with prostate cancer who underwent radical prostatectomy between 2000 and 2013 were analysed. Using S100 protein immunohistochemistry assisted in the detection of nerves. In the area of closest proximity of the tumour to the dorso-lateral margins, nerves were counted and the infiltration of nerves was categorised (0-3). Category 0 was nerves without immediate tumour-cell-contact. All nerves being fully surrounded by tumour (classical perineural carcinosis) were categorised group 3. Two further categories discriminated between nerves that were touched either by carcinoma cells below 50% of the circumference (category 1) or above (category 2). Perineural carcinosis (Pn1) was seen in 61.4% of cases and correlated positively with ISUP grades, pT categories and presence of intraductal carcinoma but failed significance on Kaplan-Meier analysis. A more quantitative analysis of percentual perineural involvement did demonstrate significant survival differences: cases with less than one Pn1-positive nerve in 5 high power fields had longer survival times. Incomplete perineural involvement (category 1-2) did not have a prognostic value, endorsing the current definition of perineural carcinosis as full circumferential encasement of a nerve by tumour cells. A quantitative analysis of the percentage of nerves positive for perineural invasion has a higher prognostic value than the classical dichotomous statement on the mere presence of perineural invasion.