Traditionally, there were three grades of vulvar intraepithelial neoplasia (VIN). However, there is little evidence that all three grades are part of the same biologic continuum or that Grade 1 is even a cancer precursor. In 2004, the International Society for the Study of Vulvar Disease changed its terminology, reserving the designation VIN for two categories of lesions based on morphologic appearance:
Usual-type VIN: Human papillomavirus (HPV)-associated Grades 2 and 3 of warty, basaloid, or mixed histology, and usually occurring in young women.
Differentiated-type VIN: non-HPV-associated Grade 3, and usually occurring in older women.
The term VIN 1 was eliminated. Disease that was previously called VIN 1 (grade I) is generally observed without definitive treatment.
High-grade VIN is usually managed with active therapy because of a higher risk for progression to invasive disease. Estimates of progression rates are imprecise. A systematic literature review that included 88 untreated patients with VIN 3 reported a 9% progression rate (8 of 88 patients) to invasive vulvar cancer during 12 to 96 months of observation. In the same review, the spontaneous regression rate was 1.2%, all of which occurred in women younger than 35 years. However, in a single-center study, 10 of 63 (16%) untreated women with VIN 2 or VIN 3 progressed to invasive cancer after a mean of 3.9 years.
VIN lesions may be multifocal or confluent and extensive. It is important to perform multiple biopsies in treatment planning to exclude occult invasive disease. VIN located in nonhairy areas can be considered an epithelial disease; however, VIN occupying hairy sites usually involves the pilosebaceous apparatus and requires a greater depth of destruction or excision because it can track along hair roots.
The principal treatment approach is surgical, but there is no consensus on the optimal surgical procedure. The goal is to remove or destroy the entire VIN lesion while preserving vulvar anatomy and function. Simple vulvectomy yields a 5-year survival rate of essentially 100% but is seldom indicated. Other more-limited surgical procedures, including separate excision of multiple lesions, are less deforming. The choice of treatment depends on the extent of the disease and the preference or experience of the treating physician. There are no reliable data comparing the efficacy and safety of the various surgical approaches.