Ameloblastic fibrosarcoma (AFS) is an extremely rare malignant odontogenic tumor characterized with benign ameloblastic cells islands and malignant mesenchymal component. While two-thirds of AFS seem to arise de novo, but one-third develops from recurrent ameloblastic fibroma (AF) or ameloblastic fibro-odontomas (AFO). Pathological distinction of malignant transformation is essential for appropriate treatment. The patient was a 28 years old man. Since the primary tumor was excised, the mass recurred 2 years later. The recurrent tumor was diagnosed as AFS. Chief complaint was pain in the right mandible. Computer tomography finding revealed multilocular intrabony lesion with radiopaque substance in the primary lesion. In the recurrent lesion cortical bone destruction was found. Microscopically, both the primary and recurrent lesions showed benign ameloblastic follicles with myxoid or highly cellular mesenchymal proliferation. The histological difference between primary and recurrent lesions were that foci of dental hard tissue composed of enamel and dentin were found only in the primary lesion, whereas nuclear pleomorphism was aggrevated in the recurrent lesion. The histological criteria determining malignancy were discussed.

• Bazarsad Shadavlonjid(Department of Oral Pathology, Oral Cancer Research Institute, Yonsei University College of Dentistry Dental School of Mongolian National University of Medical Science)
• Eunae Cho(Department of Oral Pathology, Oral Cancer Research Institute, Yonsei University College of Dentistry) | 조은애
• Woong Nam(Department of Oral and Maxillofacial Surgery, Yonsei University College of Dentistry) | 남웅
• Hyun Sil Kim(Department of Oral Pathology, Oral Cancer Research Institute, Yonsei University College of Dentistry) | 김현실
• Jong In Yook(Department of Oral Pathology, Oral Cancer Research Institute, Yonsei University College of Dentistry) | 육종인
• Jin Kim(Department of Oral Pathology, Oral Cancer Research Institute, Yonsei University College of Dentistry) | 김진 Correspondence