Primary intraosseous squamous cell carcinoma in pre-existing keratocystic odontogenic tumor: A case report and literature review.

Primary intraosseous squamous cell carcinoma (PIOSCC) is a rare type of odontogenic carcinoma that arises within the jaws. PIOSCC has no initial connection with oral mucosa and possibly develops from the residues of the odontogenic epithelium or from an odontogenic cyst or tumor. The diagnosis of PIOSCC can be difficult as it must be differentiated from other odontogenic carcinomas, such as malignant ameloblastoma, from SCCs arising from the overlying oral mucosa, from the primary tumors of the maxillary sinus or nasal mucosa, and from the tumors that have metastasized to the jaws from other primary sites. The present study reported a rare case of a 59-year-old male patient with a course of keratocystic odontogenic tumor for 25 years, between 1988 and 2013, which eventually transformed into PIOSCC after at least five recurrences and corresponding treatments. The mandible excision and titanium plate reconstruction was performed. Follow-up examinations have revealed no sign of recurrence thus far. The present study discussed this case from three aspects of clinical history, radiological examination and pathological features.