Table 1.

Evolution of classification systems for vulvar intraepithelial neoplasia (VIN)

Study	Classification
Bowen (1912) [1]	Squamous intraepithelial lesions
Kaufman (1965) [1]	Premalignant lesions into three categories: Queyrat’s erythroplasia, bowenoid carcinoma in situ and carcinoma simplex
International Society for the study of vulvar disease (ISSVD) (1976) [2]	-Carcinoma in situ and vulvar atypia -VIN 1 (mild dysplasia), VIN 2 (moderate dysplasia), and VIN 3 (severe dysplasia)
WHO classification (2003) [3]	Three subtypes: VIN 1, 2, and 3
ISSVD (2004) [4,5]	2-tier classification for squamous VIN: usual type and differentiated type VIN
Lower anogenital squamous terminology (2013) [12]	-Human papillomavirus-associated squamous lesions -Two-tier terminology: ‘low-grade squamous intraepithelial lesion (LSIL)’ and ‘high-grade squamous intraepithelial lesion (HSIL)’
ISSVD (2015) [14]	LSIL, HSIL, dVIN

WHO, World Health Organization; dVIN, differentiated vulvar intraepithelial neoplasia.