Use of the monoclonal antibody MOC-31 as an immunomarker for detecting metastatic adenocarcinoma in effusion cytology

BACKGROUND:

MOC‐31 is an established immunologic marker with which to detect adenocarcinomas. The objective of the current study was to evaluate the use of MOC‐31 in the diagnosis of metastatic adenocarcinoma in effusion specimens.

METHODS:

The authors evaluated cytologic specimens of effusions/washings in which MOC‐31 immunostaining was performed on unstained cell block sections or Papanicolaou‐stained cytospin preparations. Membranous staining with or without cytoplasmic staining was considered to be positive. The immunostaining results were correlated with the cytologic diagnoses and clinical follow‐up data.

RESULTS:

A total of 215 effusions and washings were identified (cell blocks in 162 cases, cytospin preparations in 53 cases, and both in 2 cases in which MOC‐31 immunostaining was performed). A total of 94 (44%) of the 215 cases were found to be positive for malignancy, including 87 metastatic adenocarcinomas. Specimens were positive for MOC‐31 in 76 (87%; 55 cell blocks and 21 cytospin preparations) of 87 cases of metastatic adenocarcinoma. Eleven cases of metastatic adenocarcinoma were found to be negative for MOC‐31 (4 cases from lung tumors, 2 from stomach tumors, 2 from colon tumors, 2 from breast tumors, and 1 from a renal tumor). Minimal and/or focal cytoplasmic staining for MOC‐31 was noted in 13% of cases of reactive mesothelial cells/mesothelioma. The sensitivity of MOC‐31 for metastatic adenocarcinoma was 89%, the specificity was 100%, the negative predictive value was 92%, and the positive predictive value was 100%.

CONCLUSIONS:

MOC‐31 alone was found to be highly sensitive for distinguishing reactive mesothelial cells/mesothelioma from metastatic adenocarcinoma in effusion specimens. Interpreting membranous MOC‐31 staining as positive can help prevent confusion between reactive mesothelial cells/mesothelioma and metastatic adenocarcinoma. Cancer (Cancer Cytopathol) 2011;. © 2011 American Cancer Society