KIN and cervical intraepithelial neoplasia: Due to its similarity with cervical intraepithelial neoplasia in terms of biological behavior and progression, a clinical classification of AK in keratinocytic intraepithelial neoplasia (KIN) of three histo-morphological grades (‘low grade’ or KIN I, ‘intermediate grade’ or KIN II, and ‘high grade’ or KIN III) has been proposed [6,7].