Vulvar squamous cell carcinoma and lichen sclerosus.

There are two clinicopathological types of vulvar squamous cell carcinoma, human papillomavirus (HPV)-positive and HPV-negative, which can be distinguished to some degree on routine histology. Human papillomavirus-positive carcinomas account for one-quarter to one-third of cases, occur in women on average 20 years younger than in HPV-negative, and are associated with multiple lower genital tract neoplasia. Human papillomavirus negative carcinoma is linked to lichen sclerosus. Of all carcinomas, 7-96% show lichen sclerosus in skin adjacent to the carcinoma, the majority being the first presentation of lichen sclerosus, and up to 5% of patients with lichen sclerosus develop carcinoma after long-term follow up. Where lichen sclerosus is associated with malignancy, it is often hyperplastic, may show a subtle form of intraepithelial neoplasia termed 'differentiated vulvar intraepithelial neoplasia', and may lose its pathognomonic oedematous-hyaline layer. The local additional factors causing lichen sclerosus to develop malignancy on the vulva are not known.