RESUMEN
Ameloblastic fibrosarcoma is a rare malignant odontogenic tumour characterized by a benign epithelial component within a malignant fibrous stroma. Its behaviour is relatively benign, with absence of metastatic disease, and the prognosis is reported to be good. It is a paradoxical neoplasm with "sarcomatous" morphological and immunohistochemical patterns but with a favourable clinical course. We report a new case of this tumour in a mandibular ramus of a 31-years-old male patient, that was surgically excised and treated with adjuvant chemotherapy and radiotherapy. Five years later the patient is free of disease. The growth potential of ameloblastic fibrosarcoma is evaluated and compared with a related lesion, the ameloblastic fibroma. The sarcomatous mesenchymal component of ameloblastic fibrosarcoma is positive to Ki67, PCNA and p53, in front of the negativity of ameloblastic fibroma.