PERIPHERAL KERATOAMELOBLASTOMA/SOLID KERATOCYSTIC ODONTOGENIC TUMOR

IntroductionKeratoameloblastoma (KAB) is considered a rare variant of ameloblastoma (AMEL). Three histomorphologic types exist: a) simple (acanthomatous ameloblastoma), b) complex with features of both AMEL and keratocyst odontogenic tumor (KOT/OKC), and c) papilliferous revealing papillary keratin-containing extensions in cystic ameloblastomatous lumina. There are two opposing theories on the development of KAB; 1) the tumor arises de novo as an ameloblastoma with exuberant keratin production, and 2) ameloblastomatous transformation occurs in preexisting KOT/OKC. Rare reports exist of solid KOT/OKC (SKOT) sharing features with KAB suggesting a hybrid lesion. Recently, it has been suggested that KAB should be reclassified as SKOT based on the presence of ptch1variants. Herein, we present a peripheral odontogenic tumor with features of KAB and SKOT.Materials and Methods54-year-old male presented with a firm tender swelling of the right side of maxilla in the area of the premolars causing saucerization of the alveolar bone.ResultsOriginating from surface epithelium, the tumor exhibited plexiform, follicular and cystic growth patterns with features encountered in KOT/OKC and stellate reticulum areas and reverse polarization in the periphery. Foci of mild pleomorphism and a few scattered mitoses were noted. Plexiform and cystic areas featured abundant keratin. Elongated lingulae infiltrating the connective tissue as well as plexiform extensions with predominantly ameloblastomatous features and few areas of keratinization were appreciated on the surface epithelium. The stroma revealed plasmacytic inflammation and multiple calcifications representing calcifying keratin deriving from burst cysts. Cytokeratin 19 plasmalemmal staining was observed. Keratin in calcifications was also stained. Ber-EP4 revealed focal plasmalemmal reaction in the surface epithelium with ameloblastomatous changes. There was no staining for calretinin and BRAF V600E. Variable Ki67 nuclear staining was noted.ConclusionsFeatures of KAB and SKOT were observed. Next generation sequencing for the presence of braf or ptch1 variants is underway.