Primary intraosseous odontogenic carcinoma (PIOC) is a carcinoma arising within the jaws, putatively developing from remnants of odontogenic epithelium. We describe a case of PIOC arising from odontogenic cyst affecting the left posterior mandible of 72-year-old Korean man. Clinical examination showed a symptom-free hard mass. There was no evidence of ulceration, and there was no pain or bleeding. The overlying mucosa was intact and no regional lymph nodes were palpable. Clinical and radiological studies for other distant primary sites were negative. Radiographically, the tumor showed multilocular radiolucency with a noncorticated, ill defined border surrounding an impacted third molar tooth. Histology exhibited sheets or islands of nonkeratinizing malignant epithelial cells with minimal clear cell component in continuity with begin or dysplastic cyst lining epithelium. Immunostaining for PCNA and p53 protein showed a higher percentage of positive cells and more intense staining in the carcinomatous tissues than in the benign and dysplastic lesions.

A rare case of primary intraosseous squamous cell carcinoma(PISCC) arising from lining epithelium of a dentigerous cyst is described. The case occurred at the left mandibular 3rd molar region in a 56-year-old Japanese woman. Clinical observation revealed cyst formation with an impacted 3rd molar, a common finding in dentigerous cyst, in the left mandible. Histopathologically, the lining epithelium of the cyst demonstrated transition from epithelial dysplasia to invasive squamous cell carcinoma(SCC). This case was diagnosed as PISCC arising from lining epithelium of a dentigerous cyst.