Low-grade spindle-cell ameloblastic carcinoma: report of an unusual case with immunohistochemical findings and review of the literature.

Spindle-cell differentiation in ameloblastic carcinoma is a rare event. Although reported by many authors, it was first described as a separate entity in 1999 by Slater under the heading "low-grade spindle-cell ameloblastic carcinoma." Here, we report a case of low-grade spindle-cell ameloblastic carcinoma arising in pre-existing unicystic ameloblastoma.The patient, a 60-year-old Indian woman, had a large irregular swelling in the left mandibular region. Histologically, the lesion was composed of a large cystic cavity with an ameloblastomatous lining and areas showing spindle-cell proliferation. The spindle cells showed hyperchromatism, nuclear pleomorphism, and scattered mitotic figures. To our knowledge, 6 cases of spindle-cell ameloblastic carcinoma have been published to date, and this case appears to be the first reporting malignant transformation with spindle-cell differentiation in unicystic ameloblastoma.