Squamous Cell Carcinoma of the Vulva: A Subclassification of 97 Cases by Clinicopathologic, Immunohistochemical, and Molecular Features (p16, p53, and EGFR).

Squamous cell carcinomas (SCCs) of the vulva develop through human papilloma virus (HPV)-associated or HPV-independent pathways, but the relationship between pathogenesis, classification, and prognosis of these tumors is controversial. Therefore, we review the morphology, immunophenotype, and select molecular features of a consecutive series of 97 patients with vulvar SCC with a median clinical follow-up of 3.6 years. Tumors were histologically classified as basaloid (13), warty (11), mixed basaloid and warty (1), keratinizing (68), nonkeratinizing (3), and sarcomatoid (1). Diffuse p16 expression was associated with younger age at presentation (P<0.0001), basaloid and warty carcinoma subtypes (P<0.0001), and usual vulvar intraepithelial neoplasia (P<0.0001) and was negatively associated with p53 immunopositivity (P=0.0008). Five keratinizing SCCs showed p16 and p53 coexpression, but only 1 was positive for high-risk HPV by in situ hybridization. Among 8 of 36 tumors with EGFR gene amplification, 4 were p53 positive but none p16 positive. In a Cox regression model, early clinical stage (P<0.006), p16 expression (P=0.002), and absent p53 expression (P=0.02) were independent predictors of improved overall survival. These findings utilize morphologic and immunohistochemical analysis to support HPV-associated and HPV-independent pathogenesis of vulvar SCCs and support p16 and p53 immunohistochemistry as markers of disease biology and clinical outcome.