A wide range of
tumors were immunohistochemically analyzed for alpha-1-antitrypsin (AAT) and
lysozyme in order to evaluate their specificity as histiocytic markers and their significance in the diagnostic and histogenetic evaluation of fibrohistiocytic
tumors. Besides histiocytic lesions, AAT immunoreactivity was commonly found in different types of
carcinomas and
sarcomas, and strong immunoreactivity was found in
carcinoid tumors,
malignant melanomas, and
schwannomas, which, however, had negative results for
lysozyme. The AAT immunoreactivity could be abolished with the absorption of the antibody with purified AAT also in nonhistiocytic
tumors. The neoplastic pleomorphic cells in
malignant fibrous histiocytomas (MFHs) usually had strongly positive results for AAT, whereas only entrapped histocytes had positive results for
lysozyme and for two
monoclonal antibodies to histomonocytic cells. The results show that AAT has a relatively low specificity as a histiocytic marker, and one should be careful in concluding the histiocytic nature of
tumors, such as MFHs, based on AAT immunostaining. It seems also questionable whether AAT can be used as a diagnostic marker for MFH. The reason for the widespread AAT immunoreactivity in various
tumors may be that AAT is taken up from serum to various types of nonhistiocytic
tumor cells.