Do patterns of perineural invasion improve risk stratification in prostate cancer? A narrative review

The presence of perineural invasion (PNI), typically defined as direct contact between cancer cells and nerves, is a well-established adverse prognostic factor following definitive treatment when identified on prostate needle core biopsy. In contrast, there are mixed data regarding the clinical significance of PNI detected in radical prostatectomy specimens. Beyond the mere presence of PNI in prostate cancer specimens, several studies have suggested that quantification of the number of PNI foci may provide additional prognostic information. Nonetheless, it remains controversial whether the patterns of PNI contribute meaningfully to the risk stratification of prostate cancer. Notably, the definition of PNI appears to remain inconsistent among pathologists, ranging from broad interpretations of focal tumor involvement in or around a nerve to strict criteria requiring complete circumferential nerve encirclement. This narrative review summarizes and discusses available data supporting or refuting the clinical impact of PNI patterns, including size, degree, or other morphologic features, in men with prostate cancer. Current evidence indicates that, at least on prostate biopsy, PNI patterns generally lack independent clinical utility, while significant data exist to support the prognostic relevance of PNI patterns in radical prostatectomy specimens (and several other types of solid tumors). Until further studies providing more solid evidence are available, it may be prudent for pathologists to document and consider any patterns as PNI, especially in prostate biopsy specimens.