Primary intraosseous squamous cell carcinoma with pagetoid spread arising in periapical odontogenic epithelium of the maxilla.

To date, pagetoid spread-the proliferation of pagetoid cells in intraepidermal lesions, as observed in secondary extramammary Paget's disease-has not been reported in squamous epithelium derived from the extension of head and neck carcinomas. Herein, we report a case of pagetoid squamous cell proliferation associated with a primary intraosseous carcinoma (PIOC) arising in the periapical lesion of the maxilla, a finding not reported previously. A 60-year-old man presented with prostate adenocarcinoma and bilateral pubic bone, ilium bone, and sacral bone metastases. Radiological examination revealed a cyst that enveloped the apices of the left maxillary first molar roots. Histopathological examination of the cyst specimen indicated squamous cell carcinoma; hence, PIOC was suspected and partial left maxillectomy was performed. Histopathology results showed distant epitheliotrophic spread of atypical clear cells regarding the tumor. The epitheliotrophic cells were positive for cytokeratin (CK)19 and CK7 as odontogenic markers. These phenotypes were similar to those of tumor cells, suggesting pagetoid squamous cell proliferation associated with a PIOC arising. Although diagnosis of this condition is challenging, early detection is vital to ensure prompt treatment and improve patient prognosis.