The role of immunohistochemistry in distinguishing squamous cell carcinoma from mesothelioma and adenocarcinoma in pleural effusion

BACKGROUND Distinguishing metastatic squamous cell carcinoma (SCC) from malignant mesothelioma (MM) and adenocarcinoma (ADC) in pleural effusions may be particularly challenging by routine cytologic stains. We explored the utility of using a panel of six antibodies to differentiate SCC from MM and ADC. DESIGN 33 cases of pleural cytologic preparations retrieved from our archives consisted of 9 cases of SCC, 12 cases of epithelial MM, and 12 cases of adenocarcinoma of lung. Cell blocks were prepared by the thrombin clot technique followed by formal in-fixation and paraffin-embedding. Tissue sections of 4 mu m were stained with hematoxylin and eosin and the immunoperoxidase method visualized by the biotin-streptavidin-peroxidase system. The antibodies used were cytokeratins (CAM 5.2, K903, and CK 5/6), cell membrane glycoproteins (CEA and Ber-EP4), and calretinin. In all cases, the reactivity pattern was graded on a sliding scale from 0 to 4+ according to the percentage of reactive cells. RESULTS SCC was positive for K903 (100%), CK 5/6 (89%), CAM 5.2 (78%), and CEA (22%), and negative for Ber-EP4 (100%) and calretinin (100%). MM was positive for calretinin (100%), CAM 5.2 (100%), K903 (92%), CK 5/6 (92%), and negative for CEA (100%) and Ber-EP4 (100%). ADC was positive for CAM 5.2 (100%), CEA (83%), and Ber-EP4 (83%), and negative for calretinin (100%), K903 (92%) and CK 5/6 (92%). CONCLUSIONS Our studies confirm the role of the above panel of antibodies in distinguishing among these malignancies. Positive staining for K903, CK 5/6, and CAM 5.2 separated SCC and MM from ADC. Positive staining for calretinin separated MM from SCC and ADC. Positive staining for glycoproteins and predominantly negative staining for CK 5/6, K903 and calretinin separated ADC from SCC and MM. (c) 2006 Elsevier Inc. All rights reserved.