Calcifying Odontogenic Cyst Demonstrates Recurrent WNT Pathway Mutations and So-Called Adenoid Ameloblastoma-Like Histology: Evidence Supporting Its Classification as a Neoplasm.

Calcifying odontogenic cyst (COC), once called calcifying cystic odontogenic tumor, is classified under the category of odontogenic cysts. However, the proliferative capacity of the lesional epithelium and consistent nuclear β-catenin expression raise questions about its current classification. This study aimed to determine whether COC would be better classified as a neoplasm in the histologic and molecular context. Eleven odontogenic lesions diagnosed as COC or calcifying cystic odontogenic tumor were included in this study. The growth patterns of the lesional epithelium were analyzed histologically in all cases. β-catenin immunohistochemistry and molecular profiling using Sanger sequencing and whole-exome sequencing were performed in 10 cases. Of the 11 cases studied, histologic features reminiscent of so-called adenoid ameloblastoma were observed in 72.7% (8/11), and small islands of clear cells extended into the wall in 36.4% (4/11). Intraluminal and/or mural epithelial proliferation was found in 72.7% of the cases (8/11). Nuclear β-catenin expression was observed focally in all 10 cases studied, mainly highlighting epithelial cells forming morules and adjacent to dentinoid. CTNNB1 hotspot mutations were detected in 60.0% of the cases (6/10). All the remaining cases had frameshift mutations in tumor-suppressor genes involved in the WNT pathway, including APC and NEDD4L. Recurrent WNT pathway mutations leading to nuclear translocation of β-catenin and distinct epithelial growth patterns found in COC are the neoplastic features shared by its solid counterpart, dentinogenic ghost cell tumor, supporting its classification as a tumor rather than a cyst.