Aggressive osteoblastoma of the mandible closely simulating calcifying epithelial odontogenic tumor. Report of two cases with unusual histopathologic findings.

Aggressive osteoblastoma is a rare bone-forming neoplasm composed of prominent epithelioid cells that demonstrate locally invasive growth with a high rate of recurrence but no metastatic potential. Clinical, radiographic and pathologic features of mandibular aggressive osteoblastoma in a 21-year-old African-American male and a 12-year-old Caucasian female are presented. Both tumors were resected with wide surgical margins and neither patient had adjuvant radiation or chemotherapy. The patients showed no evidence of local recurrence or distant spread either clinically or radiographically after two years of follow-up. These tumors were composed of solid sheets of pleomorphic epithelioid cells, eosinophilic amorphous osteoid with foci of calcification, which closely simulated amyloid. Differentiation of this tumor from histologically similar calcifying epithelial odontogenic tumor and low-grade osteosarcoma proved difficult. Immunohistochemical study with osteocalcin confirmed the osteoblastic nature of these epithelioid cells.