Primordial Odontogenic Tumor: A case report with histopathological analyses

Abstract

Primordial odontogenic tumor (POT) is a benign mixed epithelial and mesenchymal odontogenic tumor included into the current World Health Organization (WHO) classification of Head and Neck tumours in 2017. As far as the authors have confirmed, only eight cases of this tumor have been reported so far. This paper reports a case of POT that occurred in the right mandible of a 5-year-old patient. Panoramic radiograph showed a well-defined homogeneous radiolucency displacing the unerupted second deciduous molar to the deep part of the mandible. Histopathologically, the tumor was composed of cell-rich mesenchymal tissue with myxoid areas, surrounded by columnar epithelium and non-keratinized cuboidal epithelium in the outer layers. The histopathological diagnosis was POT. The expression patterns of cytokeratins (CK) 14, 18, 19, vimentin and CD34 suggested that the grade of differentiation of the POT was approximately equivalent to that of normal primary tooth germ tissues in cap stage to late bell stage.

Pathogenesis of primordial odontogenic tumour based on tumourigenesis and odontogenesis

“…With respect to expression of cytokeratin‐coding genes, expression of Krt 14 was higher than those of Krt 18 and Krt 19 (Figure ). These results are consistent with the observed immunoreactivity of cytokeratins in POT, that is, all epithelial layers expressed CK14, whereas CK18 and CK19 were only expressed in columnar epithelium (Mikami et al., ; Mosqueda‐Taylor et al., ). With respect to enamel organ marker protein‐coding genes of Msx2 , Jag1 , Notch1 , Sp3 , Sp6 , Alpl , the expression levels of these genes were comparatively low (FPKM < 100) (Figure ).…”

“…Msx2 expresses in the stellate reticulum (Satokata et al., ), Jag1 expresses in enamel knot and inner enamel epithelium, Notch1 and Alpl expresses in stratum intermedium (Harada et al., ), Sp3 expresses in inner and outer enamel epithelium, stellate reticulum, stratum intermedium, and ameloblast cell‐lineage (Golonzhka et al., ) and sp6 expresses in enamel knot and inner enamel epithelium, but not in stratum intermedium (Nakamura et al., ). Presence of a stellate reticulum‐like structure in the surface epithelial layers was described in the previously published POT cases (Mikami et al., ; Mosqueda‐Taylor et al., ).…”

“…The approximate differentiation stage of POT was suggested to be that of a normal primary tooth germ around the 10th to 20th week (cap stage to late bell stage) based on immunoexpression pattern of vimentin and cytokeratin18 in enamel organ and of CD34 in subepithelial mesenchymal area on POT (POT6 in this study) (Mikami et al., ). Previous reports support this hypothesis demonstrating vimentin positivity (POT1‐4 in this study, Bologna‐Molina et al., ) and CD34 positivity (POT1‐5 in this study, Bologna‐Molina et al., ; Ando et al., ).…”

“…(). Clinically, the first and/or the second deciduous molar was involved in patients in deciduous dentition stage, while the third molar was involved in patients in permanent dentition stage, suggesting that the tooth developmental factors may be related to the pathogenesis of POT (Mikami et al., ). Histopathologically, POT is composed of variable cellular to loose fibrous tissue with areas similar to dental papilla, entirely surrounded by cuboidal to columnar epithelium resembling the inner enamel epithelium without morphological evidence of odontoblast differentiation or dentine formation (Mosqueda‐Taylor et al., ).…”

“…Histopathologically, POT is composed of variable cellular to loose fibrous tissue with areas similar to dental papilla, entirely surrounded by cuboidal to columnar epithelium resembling the inner enamel epithelium without morphological evidence of odontoblast differentiation or dentine formation (Mosqueda‐Taylor et al., ). Enamel organ‐like structures are rarely observed within epithelial layers, and it was suggested that the columnar epithelium correspond to the inner enamel epithelium, and cuboidal and squamous epithelium from the middle to outer epithelial layers could correspond to outer enamel epithelium and stratum intermedium (Mikami et al., ). Immunohistochemical analysis demonstrated that the expression of Ki‐67 in the epithelium is lower than 2% while it increase up to 5% in mesenchymal components (average 3.1%) suggesting that POT is a slowly growing tumour (Bologna‐Molina et al., , ).…”