Objective: The aim of this study was to determine the immunohistochemical expression of TGF beta 1 in different types of ameloblastoma. Methods: 19 cases of ameloblastoma (10 unicystic and 9 solid ameloblastoma) were selected; 7 normal oral mucosa specimens retrieved during the extraction of impacted third molars were used as control. Of the 9 solid ameloblastomas, 7 showed a follicular pattern and 2 a plexiform pattern. All tissue specimens were fixed in 10% neutral buffered formalin (24-48 hors), processed routinely and embedded in paraffin wax.The antibody used in this study (TGF-beta RI) was obtained commercially from Santa Cruz Biotechnology Inc (Santa Cruz, CA, USA). Because substantial staining of TGF beta was also seen in the intratumoral fibrous tissue of ameloblastoma its staining intensity was assessed in both ameloblastic cells and fibrous tissue tumor. Results: In the control tissues, TGF beta positive staining was found in the connective tissue and in the epithelial mucosa. In type 1 unicystic ameloblastoma, the epithelium appeared predominantly negative. In type 2 unicystic ameloblastoma, the positivity appeared predominantly in the superficial layer of the cyst, while the endoluminal neoplastic component was negative. In type 3 unicystic ameloblastoma, the positivity appeared predominantly in the infiltrative portion of the tumor. In the solid ameloblastoma (follicular pattern) the columnar cells of the peripheral layer were positive. TGF beta 1 positive staining was detected in both cells (fibroblasts, endothelial and inflammatory cells) and intercellular components of the connective tissue in all ameloblastomas. Conclusions: These results suggest that the differences in the expression of the antigens among ameloblastoma of different histological types may be attributed to diverse factors such as the dedifferentiation of tumor cells. Such factors may also be related to extracellular matrix formation.

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