Defining incidental perineural invasion: the need for a national registry

Abstract

This article by the Perineural Invasion (PNI) Registry Group aims to clarify clinical and histopathological ambiguities surrounding PNI in non-melanoma skin cancer (NMSC). PNI is reportedly present in approxi- mately 2–6% of cases of NMSC and is associated with greater rates of morbidity and mortality. The distinc- tion between clinical PNI and incidental PNI is some- what unclear, especially in regard to management and prognosis. One important objective of the PNI Registry is to develop a standardised method of clas- sifying perineural invasion. Hence, in this article we propose a definition for PNI and for its sub- classification. This article also provides a critical analysis of the current literature on the treatment of incidental PNI by evaluating the key cohort studies that have investigated the use of surgery or radio- therapy in the management of incidental PNI. At present, there are no universal clinical guidelines that specify the acceptable treatment of NMSC exhib- iting incidental PNI. Consequently, patients often receive surgery with varying wider margins, or radio- therapy despite the limited evidence substantiating such management options. It is evident from the existing literature that current opinion is divided over the benefit of adjuvant radiotherapy. Certain prognos- tic factors have been proposed, such as the size and depth of tumour invasion, nerve diameter, the pres- ence of multifocal PNI and the type of tumour. The PNI Registry is a web-based registry that has been developed to assist in attaining further data pertaining to incidental PNI in NMSC. It is envisaged that this information will provide the foundation for identify- ing and defining best practice in managing incidental PNI.