High concordance of molecular subtyping between pre-surgical biopsy and surgical resection specimen (matched-pair analysis) in patients with vulvar squamous cell carcinoma using p16-and p53-immunostaining

Objective. Vulvar squamous cell carcinoma (VSCC) can be stratified into three molecular subtypes based on the immunoexpression of p16 and p53: HPV-independent p53-abnormal (p53abn) (most common, biologically aggressive), HPV-associated, with p16-overexpression (second most common, prognostically more favourable) and more recently recognised HPV-independent p53-wildtype (p53wt) (rarest subtype, prognostically intermediate). Our aim was to determine whether molecular subtypes can be reliably identified in pre-operative biopsies and whether these correspond to the subsequent vulvectomy specimen. Methods. Matched-paired pre-surgical biopsies and subsequent resection specimen of 57 patients with VSCC were analysed for the immunohistochemical expression of p16 and p53 by performing a three-tiered molecular subtyping to test the accuracy rate. Results. Most cases 36/57 (63.2%) belonged to the HPV-independent (p53-abn) molecular subtype, followed by HPV-associated 17/57 (29.8%) and HPV-independent (p53wt) 4/57 (7.0%). The overall accuracy rate on biopsy was 91.2% (52/57): 97.3% for p53-abnormal, 94.1% for p16-overexpression and 50% for p16-neg/p53-wt VSCC. Incorrect interpretation of immunohistochemical p53 staining pattern was the reason for discordant results in molecular subtyping in all five cases. In one case there was an underestimation of p53 pattern (wildtype instead of abnormal/aberrant) and in one case an overestimation of the p53 staining pattern (abnormal/aberrant instead of wildtype). In 3/5 there was a "double positive" staining result (p16 overexpression and abnormal/aberrant p53 staining pattern). In that cases additional molecular workup is required for correct molecular subtyping, resulting in an overall need for molecular examination of 3/57 (3.5%). Conclusions. Compared to the final resections specimen, the three-tiered molecular classification of VSCC can be determined on pre-surgical biopsies with a high accuracy rate. This enables more precise surgical planning,