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Rare tumor of the oral cavity presenting as a gingival swelling without bone involvement was present. The lesion, resected for mastication troubles, histologically presented a basaloid cell proliferation predominantly organized in nests formed by a peripheral palisading of cells with apically disposed nuclei. Immunohistochemical stainings for the cytokeratin 19 and Ber-EP4 showed a marked and diffuse positivity for the former, while the latter was negative. These results support the diagnosis of peripheral ameloblastoma and allow us to distinguish it from the basal cell carcinoma, which shares some histological features with this unusual tumor of the oral cavity.

Summary 183 cases of soft tissue tumors were studied utilizing the immunoperoxidase technique to demonstrate alpha-1-antitrypsin, ferritin and lysozyme. The series comprises SO malignant lesions, 34 intermediate malignancy lesions, 99 benign lesions of fibrohistiocytic origin, and 23 malignant tumors of non fibrohistiocytic origin. The actual results of the study are as follows: alpha-1-antitrypsin, ferritin and lysozyme were always absent in 10 fibrosarcomas, 2 liposarcomas, 2 Ewing sarcomas, 3 synovial sarcomas, 4 neuro fibrosarcomas, and 2 rhabdomyosarcomas, but in 24 malignant fibrous histiocytomas, 34 cases of dermato fibrosarcoma protuberans and 102 benign fibrohistiocytic lesions, these activities were present in a percentage that ranged between 12% and 38% (average 25%). Differences in the frequency of positive reactions did not occur between benign and malignant fibrobistiocytic lesions. The immunohistological examinations carried out have, therefore, only a very limited value for the practical diagnostic evaluation, but, when positive, are important to clarify the histogenesis of the tumor.