Widespread immunoreactivity for alpha-1-antichymotrypsin in different types of tumors.

The presence of alpha-1-antichymotrypsin (AACT) immunoreactivity was investigated in a broad range of different tumors. Because optimal AACT immunoreactivity of histiocytes was achieved by use of a protease pretreatment of paraffin sections, all tumors were studied by using pepsin treatment of the sections. In such conditions, more than 80% of different carcinomas, sarcomas, melanomas, and lymphomas were positive for AACT. The results indicate that AACT immunoreactivity is not specific for histiocytic tumors and therefore cannot be used as a histiocytic marker and to substantiate the concept of histiocytic nature of tumors, such as malignant fibrous histiocytoma. The concept of AACT as a histiocytic marker may be based on the fact that histiocytes, for some reason, stain more intensively for AACT, and immunoreactivity can also be found in them at unoptimal immunostaining conditions.