Central granular cell odontogenic tumour: report of the first malignant case and review of the literature.

Granular cell odontogenic tumours (GCOT) are rare neoplasms that usually manifest a benign clinical behaviour. We document the first case of GCOT exhibiting clinico-pathological features of malignancy that occurred in the maxilla of a 40-year-old male. The lesion appeared as an intra-oral polypoid mass and, at CT scan, as a poorly demarcated radiolucency eroding the cortical plate. Histologically, the tumour consisted of clusters of granular cells, exhibiting nuclear pleomorphism, prominent nucleoli and mitotic figures, and spindle cells in a collagenous stroma containing cementicles and strands of odontogenic epithelium. Morphologic transition from fibroblast-like to granular cells was frequently detected. The tumour cells extensively invaded the oral and respiratory mucosae and the adjacent soft tissues and exhibited vimentin and CD 68 immunoreactivity and high (21%) Ki 67 immunolabeling but not cytokeratins, E.M.A. actin, desmin, myosin or S-100 protein positivity. The patient experienced tumour recurrence 16 months after radical surgery. While the histogenesis of GCOT remains to be clarified, we document the existence of a malignant counterpart of this tumour and propose the name of malignant GCOT or granular cell odontogenic sarcoma for such entity.