A case of mandibular bone metastasis of ameloblastoma from the opposite side of mandible: Immunohistochemical and genetic analyses of clonality

A 46-year-old male visited our hospital for examination and treatment of a right mandibular tumor. Before this visit, he had undergone extirpation five times after diagnosis of right mandibular ameloblastoma by a local doctor. The recurrent ameloblastoma invaded into wide area of right mandible, the oral floor and the skin. The tumor was surgically resected, and complete resection was confirmed histopathologically. However, 1 year and 10 months after initial surgery, another tumor (ameloblastoma) developed in the opposite side of mandibular molar region. The left lesion was also surgically resected with tumor free margin. Histopathology of both lesions were similar, and immunostaining was positive for CK19, CK7 and AE1/3 and negative for Ber-Ep4 in the left and right lesions. Partial expression of p16 in odontogenic epithelial cell clusters in both lesions. BRAF (V600E) mutation could be detected in the left lesion. According to the results of immunohistochemistry and the similarity of the histopathology, we strongly considered that the recurrent left mandibular lesion was a metastasis from the right lesion. Both the right (primary) lesion and the left (metastatic) lesion had histopathologically low cellular atypia and were diagnosed as benign lesions. However, this case showed that lesions of ameloblastoma with repeated recurrence and extensive invasion could have metastatic potential and required strict follow-up.