CDKN1B and squamous cell intraepithelial neoplasia: According to the relationship between phospho-p27 expression and proliferation, in low grade SIL the dysplastic basal and parabasal cells were in most instances positive for the expression of both pThr187-p27 (Figure 2A), and Ki-67; these were instead negative for "plain" p27 whose staining was confined to the intermediate and superficial squamous cells, as described [15].