Aim: Peripheral ameloblastoma (PA) is a rare variant of ameloblastoma occurring in the extraosseous region. With regard to the histogenesis of the tumor, two major sources of origin are considered: odontogenic epithelial remnants and the gingival epithelium. In this study, we examined the immunohistochemical profiles of cytokeratins (CKs) and Ki-67 labeling index (LI) of PAs, and discuss the histogenesis and the biologic behavior of the PA.
Materials and methods: Eight cases of PA were retrieved from the pathology files of 212 cases of ameloblastoma that had been registered at our hospital. Immunohistochemical staining was performed in seven cases using monoclonal antibodies of six CKs (7, 8, 13, 14, 18, and 19) and Ki-67.
Results: All cases of PA expressed CK13, 14, and 19. CK18 was positive staining in six cases, and CK8 in five cases. This staining pattern was similar to that in intraosseous ameloblastomas (IAs). The mean of Ki-67 LI of PAs (1.91%) was significantly lower than that of IAs (4.82%) (P = 0.002).
Conclusion: We consider that the PA originates from odontogenic epithelial remnants rather than from the gingival epithelium, and the Ki-67 LI of the tumor is a good prognostic indicator.