Squamous vulvar intraepithelial neoplasia: 2004 modified terminology, ISSVD Vulvar Oncology Subcommittee.

In the current classification, squamous vulvar intraepithelial neoplasia (VIN) is categorized as VIN 1, 2 and 3 according to the degree of abnormality. There is neither evidence that the VIN 1-3 morphologic spectrum reflects a biologic continuum nor that VIN 1 is a cancer precursor. The VIN 2 and 3 category includes 2 types of lesion, which differ in morphology, biology and clinical features. VIN, usual type (warty, basaloid and mixed), is HPV related in most cases. Invasive squamous carcinomas of warty or basaloid type is associated with VIN, usual type. VIN, differentiated type, is seen particularly in older women with lichen sclerosus and/or squamous cell hyperplasia in some cases. Neither VIN, differentiated type, nor associated keratinizing squamous cell carcinoma is HPV related. The term VIN should apply only to histologically high grade squamous lesions (former terms, VIN 2 and VIN 3 and differentiated VIN 3). The term VIN 1 will no longer be used. Two categories should describe squamous VIN: VIN, usual type (encompassing former VIN 2 and 3 of warty, basaloid and mixed types) and VIN, differentiated type (VIN 3, differentiated type).