Prostatic adenocarcinoma. Evaluation of immunoreactivity to monoclonal antibody B72.3

Monoclonal antibody B72.3 reacts with a tumor-associated glycoprotein designated TAG-72 that is expressed in many adenocarcinomas but not in normal tissues. The authors evaluated the immunoreactivity of B72.3 to benign, hyperplastic prostate, and to primary adenocarcinoma of the prostate to determine the frequency of TAG-72 production by benign and malignant prostatic epithelium. Focal cytoplasmic staining of gland cells was seen in 19 of 20 cases of glandular hyperplasia, and weak, homogeneous staining of secretions was seen in five cases. In contrast, 27 of the 35 (77%) adenocarcinomas studied showed at least focal intense staining of secretions, and 30 (86%) of the tumors showed some cytoplasmic immunostaining with B72.3. Positive staining occurred in all of the well-differentiated adenocarcinomas (100%) but was seen less often in moderately differentiated (82%) and poorly differentiated adenocarcinomas (58%). Because benign gland cells may express the TAG-72 antigen, immunohistochemistry results must be interpreted with caution and with regard to the overall morphologic pattern. Nonetheless, a positive B72.3 immunostain may be useful in identifying adenocarcinoma of the prostate, especially when an intense luminal reaction is found. A negative stain does not exclude the presence of adenocarcinoma, however.