Molecular Subtypes of Vulvar Squamous Cell Carcinoma: the significance of HPV-independent/p53 Wild Type

Vulvar carcinoma is a rare disease, meeting the criteria of a “rare cancer”. The incidence has been increasing, especially in women <60 years of age. Squamous cell carcinoma (VSCC) accounts for an overwhelming majority of vulvar carcinomas and is the focus of this review. As with many cancers, the increased understanding of molecular events during tumorigenesis has led to emergence of molecular subclassification of VSCC, which is subclassified into those tumors arising secondary to high risk human papillomavirus infection (HPV associated, or HPVa) and those which arise independent of HPV (HPVi), most commonly in the setting of a chronic inflammatory condition of the vulvar skin. This latter group of HPVi VSCC arises in most cases secondary to mutations in TP53, but recently attention has focused on the uncommon TP53 wildtype HPVi VSCC. These three molecular subtypes of VSCC (HPVa, HPVi p53 abnormal, HPVi p53 wild type), and their precursor lesions, cannot be diagnosed based on routine histopathological examination and immunostaining for p53 and p16, as surrogate markers for TP53 mutation and high-risk HPV infection, respectively, is essential. Molecular subtyping of VSCC shows high reproducibility and provides important prognostic information. The HPVa VSCC have the most favorable prognosis while the HPVi VSCC with TP53 mutations (p53abn) have the worst prognosis, and the HPVi VSCC with wild type TP53 (p53wt) have an intermediate prognosis. In this review, we discuss the evidence supporting this molecular subclassification and its implications for diagnosis and treatment of VSCC and its precursors.