Squamous Vulvar Intraepithelial Neoplasia: 2004 Modified Terminology, ISSVD Vulvar Oncology Subcommittee

The terminology for squamous vulvar intraepithelial neoplasia (VIN) was established in 1986 by the International Society for the Study of Vulvar Disease (ISSVD). In this classification, abnormal changes in vulvar tissue seen on cytology are categorized as VIN 1, VIN 2, or VIN 3. Although the grading is similar to that used for cervical intraepithelial lesions (CIN), there is no evidence that VIN and CIN have a similar natural history or that the grading of VIN represents a biologic continuum. It is now accepted that VIN 1 has a low malignant potential and is not a precursor to VIN 2 or 3. As originally described, VIN 1 denotes basally cellular changes in the basal epithelial that are relatively uncommon and are an effect of exposure to human papillomavirus (HPV). Its diagnosis varies from pathologist to pathologist and is not reproducible. The categories of VIN 2 and VIN 3 have been useful in describing high-grade disease, but they do not differentiate between lesions usually associated with high-risk HPV types (VIN, usual type) and other lesions not resulting from exposure to HPV (VIN, differentiated). The ISSVD proposal for vulvar intraepithelial neoplasia uses the term VIN for all high-grade squamous lesions. Two different categories of VIN are to be used VIN, usual type, is related to HPV. It is further subdivided into 3 histologic subtypes: warty, basaloid, and mixed. These lesions are unifocal or multifocal and may present clinically as patches, erosion, plaques, papules, and nodules with hyperkeratotic, verrucous, pigmented red or white changes. The progression of VIN, usual type, to invasive cancer in untreated patients has been unequivocally demonstrated, especially in women over 30 years of age or immunocompromised women. A variant of VIN, usual type, associated with genital warts or pregnancy is seen in some younger women and can regress spontaneously. VIN, differentiated type, is not associated with HPV and is related to lichen sclerosa and/or squamous cell hyperplasia. It is a less common diagnosis usually seen in older women. It usually presents as a warty papule or hyperkeratotic plaque. It is commonly seen during follow up of women who have been treated for lichen sclerosus or invasive vulvar cancer. Rarely, a pagetoid type of VIN is seen that cannot be classified as either VIN, usual type, or VIN, differentiated type. This type of VIN can be termed VIN, unclassified.