OBJECTIVE: To determine the diagnostic value of the BCA-225 antibody in discriminating adenocarcinoma from benign mesothelium in body cavity effusions.

STUDY DESIGN: One hundred four cases of unequivocally benign (34 cases) and malignant (70 cases) serous effusions with cell block material were immunostained for BCA-225 using the ABC method without antigen retrieval. The percentage of positively staining cells in each case was estimated in a blind fashion.

RESULTS: BCA-225 stained at least 10% of morphologically malignant cells in 28 of 32 (88%) breast carcinomas and 58 of 67 (87%) adenocarcinomas overall. Neuroendocrine carcinomas (two cases) and one mesothelioma were positive in < or = 5% of their respective tumor cells. Of 34 benign cases, 6 (18%) exhibited positive staining, albeit in rare, morphologically benign cells.

CONCLUSION: BCA-225 is able to discriminate adenocarcinoma from reactive mesothelium in cell block preparations and may prove useful as part of an antibody panel.