SOX2 and cervical squamous intraepithelial neoplasia: One of the first steps in the carcinogenic process in the uterine cervix is HPV infection of the basal cells of (metaplastic) squamous epithelium, reserve cells underlying the columnar epithelium in the transformation zone or cuboidal squamocolumnar junctional (SCJ) cells in the endocervix, after which SOX2-positive squamous CIN lesions arise.