Ameloblastic fibroma and BRAF V600E immunohistochemistry staining pattern: case report and review of a rare entity

Ameloblastic fibroma is a rare, benign, biphasic odontogenic tumour that typically presents in young patients and is treated conservatively with an excellent prognosis. An important differential is ameloblastoma, a more common odontogenic neoplasm that shares many of the clinical, radiological, and histological features, but requires more extensive surgery due to its potentially destructive nature. Both tumours demonstrate BRAF V600E mutations. While epithelial staining with BRAF V600E-specific immunohistochemistry is considered a surrogate marker for mutation and is supportive of the diagnosis of ameloblastoma, the staining pattern in ameloblastic fibroma has not been defined previously because of the rarity of the lesion. This report describes a case of ameloblastic fibroma in a 13-year-old, in which BRAF V600E immunohistochemistry showed cytoplasmic staining in both the stromal and epithelial components of the tumour. On review of the literature, this was interpreted to be concordant with the biphasic nature of the lesion.