Transformation of odontogenic keratocyst into a solid variant of odontogenic keratocyst/keratoameloblastoma. Mammalia

Keratoameloblastoma (KA) and solid variant of odontogenic keratocyst (SOKC) are rare odontogenic lesions, and their relationship and differences are controversial. In this report, we aimed to describe a case that started as an odontogenic keratocyst (OKC) and transformed to SOKC/KA upon recurrence. A 26-year-old male who presented with swelling in the right cheek was referred to our department. At the initial visit, unicystic bone permeation images were observed extending from the right canine to the molar, maxillary sinus, and nasal cavity. After the biopsy, the patient underwent excisional surgery and was diagnosed as OKC. Thereafter, the lesion recurred six times over a period of 13 years and showed different histopathological features from those of the primary lesion, all consisted of numerous cysts with keratinization and were diagnosed as SOKC/KA. The Ki-67 positivity rate was approximately 10%, which was higher than that of the primary lesion, but there was no atypia. Genetic analysis of the recurrent lesion revealed mutations in APC and KRAS. This case originated from OKC, and the morphological features of OKC and KA were mixed upon recurrence, supporting the commonality and association between the two. However, multiple mutations different from those of OKC and ameloblastoma were detected, suggesting an association with increased proliferative activity and a high recurrence rate.