PCNA and odontogenic cyst: Previous studies have shown that the epithelial lining of OKCs has increased proliferation potential compared with that of other types of odontogenic cysts, i.e. dentigerous cysts and radicular cysts.3,5 Particularly, those with PTCH1 truncation-causing mutations had higher proliferative activity than OKCs with non-truncating mutations or WT PTCH1, based on immunohistochemical staining for Ki67 and/or PCNA.41 In this study, we verified that PTCH1R135X/+ cells have increased proliferative ability, as shown by CCK-8 assays using the PTCH1R135X/+ hESC-Es model.