Ameloblastoma is a locally invasive, histologically nonmalignant tumor that may 
on very rare occasions give rise to metastases. A patient with a mandibular 
ameloblastoma presenting typical histologic appearances developed a pulmonary 
metastasis confirmed by histology as arising from the primary tumor. Two groups 
of these extremely rare malignant ameloblastomas can be distinguished: those 
without histologic signs of degeneration that give rise to metastases identical 
to the primary lesion, and those with degenerative signs provoking metastases 
with the histologic appearance of undifferentiated carcinoma. No relation 
appears to exist between size of primary tumor, histologic type of 
ameloblastoma, or its course and tendency to produce metastases.