Utility of MOC-31 monoclonal antibody in differentiating metastatic adenocarcinoma cells and reactive mesothelial cells in effusion cytology.

In effusion cytology, a clear distinction between reactive mesothelial cells and metastatic adenocarcinoma cells is sometimes challenging mainly due to similarities in the cytomorphological features. In such cases for definitive diagnosis, paraffin-embedded cell block examination and immunohistochemistry are helpful in making this distinction. MOC-31 is one of the proposed immunomarker for adenocarcinoma cells. We undertook to evaluate the role of MOC-31 as a marker for identifying adenocarcinoma cells in effusion specimen. A total of 185 paraffin-embedded cell blocks of effusion samples were identified, of these 111 cases were of metastatic adenocarcinoma. MOC-31 was positive in 101 of the 111 cases of metastatic adenocarcinoma. Minimal focal cytoplasmic staining was also seen in 7 of the 74 cases of reactive mesothelial cells, but these were taken negative as they did not show membrane positivity. The sensitivity and specificity of MOC-31 for metastatic adenocarcinoma cells were 92.5%, and 100% respectively, positive and negative predictive value (NPV) was 100% and 91.14%, respectively. MOC-31 can be used as a reliable marker in effusions for distinguishing metastatic adenocarcinoma from reactive mesothelial cases.