MOC-31 aids in the differentiation between adenocarcinoma and reactive mesothelial cells

BACKGROUND. Evaluation of effusion specimens for the presence of adenocarci noma often is complicated by the presence of reactive mesothelial cells tha t can mimic adenocarcinoma. Ancillary studies, in particular immunohistoche mistry, can be helpful in making this distinction. MOC-31 is an antibody th at recently was reported to be useful in distinguishing adenocarcinoma from mesothelioma in tissue specimens. In this study we examined the utility of this antibody in pleural effusions. METHODS. Eighty-nine archival, formalin fixed, paraffin embedded cell block s representing 59 adenocarcinomas, 12 other neoplasms (including 6 mesothel iomas), and 18 reactive effusions were retrieved. After protease digestion, recut slides were immunostained with the MOC-31 antibody utilizing a modif ied avidin-biatin complex technique. Only membrane-based reactivity was con sidered as positive. RESULTS. In two adenocarcinomas there was insufficient material remaining i n the cell block Among the 57 remaining cases, reactivity was observed in 5 4 cases. Reactivity also was observed in one of six mesotheliomas and one s mall cell carcinoma. The remaining cases, including all 18 reactive effusio ns, were nonreactive. In distinguishing adenocarcinoma from reactive mesoth elial cells, the presence of MOC-31 reactivity was found to be 95% sensitiv e and 100% specific with a positive predictive value of 100% and a negative predictive value of 95%. CONCLUSIONS, MOC-31 is useful in differentiating between adenocarcinoma and reactive mesothelial cells in pleural effusion specimens. Cancer (Cancer C ytopathol) 1999;87:390-4. (C) 1999 American Cancer Society.