Ameloblastoma arising in odontogenic keratocyst: report of four rare cases, immunohistochemical analysis and review of literature

Odontogenic keratocyst (OKC) is a developmental cyst of the gnathic bones arising from the rests of dental lamina. This cyst demonstrates propensity for aggressive behavior and a relative high rate of recurrence compared to the other odontogenic cysts. Ameloblastoma is a benign neoplasm of odontogenic epithelium. It is the most common clinically significant odontogenic tumor that may demonstrate a locally aggressive clinical behavior. Ameloblastoma may theoretically arise de novo from the rests of dental lamina as well as a developing enamel organ or from the epithelial lining of a pre-existing odontogenic cyst. Rare cases of ameloblastoma arising in the wall of dentigerous cyst, calcifying odontogenic cyst, glandular odontogenic cyst, radicular cyst, and residual cyst have been previously documented in the existing literature. Furthermore, ameloblastomatous changes of cysts in nevoid basal cell carcinoma syndrome (NBCCS) have been previously reported. To our knowledge, only one case of ameloblastoma combined with an OKC in a non-syndromic patient has been reported in the English language literature so far. Here we report four additional and extremely rare instances of ameloblastoma arising in combination with an OKC. Microscopically, all the cases exhibit the distinctive histopathologic features of OKC and ameloblastoma. Immunohistochemical staining for CD56, which has been reported to stain the peripheral layer of ameloblastomas and calretinin was performed on all cases. Additionally, two OKCs were stained with both markers as controls. No case demonstrated calretinin positivity, including in the obvious ameloblastic islands. CD56 highlighted only the ameloblastic areas while the areas of OKC were negative. The lack of staining in the areas typical of OKC help highlight the combined nature of the lesions. These findings suggest that much may still be unknown about the biologic potentials of OKC and that the pluripotentiality of the odontogenic epithelium may be the driving force behind such rare findings.