Murine monoclonal antibody F36/22 was derived by immunizing BALB/c mice with human breast cancer cells. This antibody reacts with an antigen located both on differentiated mammary ductal epithelia and on breast carcinomas, as examined by indirect immunoperoxidase techniques. Although the expression of this antigen correlated with estrogen receptor levels of breast tumors, antibody F36/22 did not directly react with estrophilin. In contrast to the expression of classical differentiation antigens, this antigen was found in a high percentage of poorly differentiated carcinomas of the breast. Staining intensities were similar for well- and poorly differentiated tumors; thus, antigen expression was not related to tumor grade. Intratumoral heterogeneity of antigen expression was observed in the majority of tumors. Since a subset (64 of 80) of the breast carcinomas examined have expressed the antigen, McAb 36/22 was of use for the immunological subclassification of tumors which were indistinguishable by conventional histopathological staining techniques. The antigen was also present on other adenocarcinomas (ovary, colon, stomach, pancreas, and prostate); however, these tumors usually exhibited reduced staining intensity compared with that observed in breast cancer. The normal counterpart tissues at these histotypes contained no detectable levels of the antigen, and increased expression of the antigen was associated with tumorigenesis at these sites. Tumors of mesenchymal origin and carcinomas other than adenocarcinomas exhibited undetectable levels of the antigen. Therefore, depending on the organ site, McAb F36/22 recognizes an epithelial and/or tumor-associated antigen.

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Supported in part by NIH Grants CA 34346, CA30370, and CA 25653 and by a State University of New York at Buffalo Graduate Research Access Development Grant.

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