Clinicopathological investigation of odontogenic fibroma in tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant inherited disease characterized by systemic hamartoma and diverse systemic features. TSC1 and TSC2 are the causative genes, and mental retardation, epileptic seizures, and facial angiofibroma develop in many patients with the disease. The case of a patient with TSC who developed a central odontogenic fibroma of the mandible is reported here. The patient was a 21-year-old woman who was referred with a swelling of the labial gingiva in the region of the right lower lateral incisor and canine. Dental radiography revealed a multilocular radiolucent region with a clear boundary. The right lower lateral incisor and canine were continuous with the lesion and thus were excised en bloc. The lesion was encapsulated and easily dissected. The diagnosis on immunohistological staining was odontogenic fibroma without an epithelial component. TSC1/2 gene mutation causes abnormal activation of mammalian target of rapamycin (mTOR) downstream of the PI3K-AKT pathway. The odontogenic fibroma in this patient was positive for mTOR, suggesting that the development of the odontogenic fibroma was the result of abnormal activation of mTOR, as in angiofibroma. The clinical course of this patient is presented and the developmental mechanism of central odontogenic fibroma is discussed.