Spindle cell variant of ameloblastic carcinoma arising from an unicystic amelobastoma: Report of a rare case.

Malignant transformation of ameloblastomas arising from an odontogenic cyst or de novo is well-recognized. Malignancies in ameloblastomas may involve metastasis or a local dysplastic change in the tissue. The latter are classified as ameloblastic carcinomas. A 75-year-old male presented with a mandibular cystic swelling, with no evidence of metastasis. Dysplastic ameloblastic cells with spindle-cell transformation were seen arising from a cystic lining with features of a unicystic ameloblastoma. Immunohistochemically the lesion stained positive with cytokeratin 8,19 and alpha smooth muscle actin, but was negative for vimentin. A diagnosis of spindle-cell ameloblastic carcinoma was made. Spindle-cell ameloblastic carcinomas are rare and this is the second case arising from a unicystic ameloblastoma reported in literature. The recognition of this transformation and inclusion of this entity in the classification of ameloblastic carcinomas is stressed.