Review of Terminology of Precursors of Vulvar Squamous Cell Carcinoma

The popular term for vulvar squamous cell carcinoma in situ/dysplasia is vulvar intraepithelial neoplasia (VIN). VIN is a histological diagnosis based on loss of squamous epithelial maturation associated with enlarged, hyperchromatic, pleomorphic nuclei and increased, usually atypical mitoses. There are two types of VIN: the usual (not otherwise specified) type, also known as warty-basaloid, and the differentiated type. There are 3 grading systems for warty-basaloid VIN: the traditional 3-grade system of VIN 1-3, a low-grade/high grade Bethesda-like system and the International Society for the Study of Vulvovaginal Disease's proposal for only 1 grade. The ISSVD system eliminates VIN 1 and combines VIN 2 and 3 on the grounds that VIN 1 has not been shown to be a reproducible diagnosis and VIN 2 and 3 are not reliably separated. The evidence supports the ISSVD proposal. Warty basaloid VIN may be sub-typed into warty and basaloid VIN. Sub-typing has clinical relevance but its reproducibility is not proven. Warty-basaloid VIN may regress. Differentiated VIN has been typically diagnosed co-incident with squamous cell carcinoma. With increased frequency of performance of biopsy of hyperplastic lesions, differentiated VIN should be diagnosed more commonly before squamous carcinoma occurs.