Squamous odontogenic tumor of the maxilla: diagnostic considerations and immunohistochemical insights into pathogenesis—a case report

Squamous odontogenic tumour (SOT) is a rare benign odontogenic epithelial neoplasm that can be mistaken for odontogenic cyst, and several benign and malignant odontogenic and non-odontogenic tumours. The rarity and histological overlap of the present case with more aggressive entities make accurate diagnosis challenging and clinically consequential, hence worth reporting. We report the case of a 51-year-old Indian woman who presented with a six-month history of a painless, gradually enlarging swelling of the right maxilla. Panoramic radiography revealed a well-circumscribed, unilocular radiolucency without evidence of cortical perforation. Histopathological examination demonstrated islands and cords of well-differentiated squamous epithelium within a mature fibrous stroma, without significant cytologic atypia. Immunohistochemistry showed diffuse nuclear p40 positivity, diffuse cytoplasmic cytokeratin-19 (CK19) positivity, and a very low Ki-67 labelling index, collectively supporting a diagnosis of SOT. The lesion was managed by conservative surgical excision and curettage. At fourteen-month follow-up, no recurrence was observed. This case highlights several diagnostically important features of SOT. Maxillary SOT is less frequent than its mandibular counterpart. The histological overlap with ameloblastoma, squamous odontogenic tumor-like proliferations in odontogenic cysts, primary intraosseous squamous cell carcinoma, and sclerosing odontogenic carcinoma necessitates rigorous clinicopathological correlation. The p40/CK19/Ki-67 immunohistochemical panel proved particularly useful in establishing a definitive benign diagnosis.