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Diagnostic utility of a homeobox transcription factor, engrailed homeobox 1 (En1) in the histopathology of salivary gland neoplasms was studied. The expression of En1 was immunohistochemically examined in 51 cases of adenoid cystic carcinoma (AdCC) and 143 cases of other salivary gland neoplasms. In all 51 AdCCs, En1 was expressed in 30–100% of tumor cells. In eight of nine polymorphous adenocarcinomas (PACs), En1 was expressed in 40–100% of tumor cells. Less than 5% of tumor cells expressed En1 in three of 12 epithelial–myoepithelial carcinomas, one of 17 basal cell adenomas (BCAs), and one of 34 pleomorphic adenomas (PAs). Among 55 other carcinoma cases, 1–30% of tumor cells expressed En1 in three salivary duct carcinomas (SDCs) ex PA. None of the myoepitheliomas and Warthin tumors expressed En1. When the cut‐off value of the percentage of En1‐expressing cells was set to 25%, all 51 AdCCs, eight of nine PACs and one SDC ex PA were En1‐positive and the others were En1‐negative. En1 is expressed consistently in AdCCs, frequently in PACs, but rarely in other salivary gland neoplasms. En1 is a possible diagnostic marker for AdCC and PAC in the histopathology of salivary gland neoplasms. [ABSTRACT FROM AUTHOR]

Primordial odontogenic tumor (POT) is a newly classified, mixed epithelial and mesenchymal odontogenic tumor, with only 17 reported cases to date. Herein, we report a case of POT that occurred in the right maxilla of a 10‐year‐old boy and reveal unique features in comparison with those previously reported. Radiologically, the lesion presented as a well‐defined, unilocular radiolucency with notable radiopaque foci on the periphery. Microscopically, the tumor was mainly composed of dental papilla‐like myxoid fibrous connective tissue, largely surrounded by non‐keratinized squamous epithelium with numerous calcified particles, and partly enclosed by inner enamel epithelium‐like columnar cells and enamel organ‐like structures accompanied with cuboidal and/or stellate reticulum‐like cells. Immunohistochemically, the epithelium tested positive for cytokeratin 14 and 19. Moreover, amelogenin and ameloblastin, matrix proteins relating to enamel formation, were positive in the covering epithelium. The tumor was enucleated as a whole, and no recurrence was recorded thereafter. Although the presence of numerous calcified particles was unique, we diagnosed this lesion as POT based on the above‐described features. Furthermore, we emphasize the importance of the differential diagnosis of POT and other odontogenic tumors that resemble corresponding tooth germ components. [ABSTRACT FROM AUTHOR]