Immunohistochemistry provides an important indicator for differential diagnosis between pleural malignant mesothelioma and lung adenocarcinoma, which have complex therapeutic and medicolegal implications. To pinpoint a reliable, restricted panel of markers, the authors evaluated the efficacy of select commercial antibodies in a series of patients with confirmed clinicopathologic diagnosis of mesothelioma or lung adenocarcinoma with the aid of multiple logistic classification tables. Specimens of 46 mesotheliomas and 20 lung adenocarcinomas were examined with calretinin, thrombomodulin, cytokeratins (CKs) 5/6, and high-molecular weight CKs (indicators of mesothelioma), alongside MOC 31, Ber-EP4, and carcinoembryonic antigen (CEA; indicators of lung adenocarcinoma). Of the mesotheliomas, 40 of 46 (87%) were positive with calretinin, 29 of 46 (63%) with thrombomodulin, 40 of 46 (87%) with CKs 5/6, and 41 of 46 (89%) with high-weight CKs; five of 46 mesotheliomas (11%) were focally reactive with MOC 31, four of 46 (9%) with Ber-EP4, and two of 46 (4%) with CEA. Of the lung adenocarcinomas, 18 of 20 (90%) were positive with MOC 31, 20 of 20 (100%) with Ber-EP4, and 17 of 20 (85%) with CEA; and two of 20 (10%) were focally reactive with calretinin, one of 20 (5%) with thrombomodulin, none of 20 (0%) with CKs 5/6, and five of 20 (25%) with high-weight CKs. Multiple logistic modeling indicated two batteries of three antibodies permitting more than 98% overall accuracy: Ber-EP4 plus CKs 5/6 plus calretinin, and Ber-EP4 plus CKs 5/6 plus CEA.

Cytokeratin (CK) patterns and albumin messenger RNA (mRNA) are investigated in 24 patients with benign hepatic lesions (7 patients with focal nodular hyperplasia [FNH], 10 with hepatocellular adenomas [HA], 1 with biliary hamartoma, 4 with biliary cysts, 2 with cystadenomas) and in 8 patients with cystadenocarcinoma, a rare liver malignancy. The lesions and surrounding tissue of the hepatocytic components expressed CK 8 and 18 at immunohistochemistry, whereas the biliary elements evidenced CK 8 and 18 and CK 7 and 19. The albumin mRNA, as detected by in situ hybridization (ISH), revealed different distributions in the hepatocytes of FNH and HA. In the benign biliary lesions, the normal hepatocytes surrounding the tumors expressed albumin mRNA, whereas the biliary structures did not. Interestingly, in the cystadenocarcinomas, albumin mRNA was observed not only in the hepatocytes of residual parenchyma, but also in neoplastic bile duct cells lining the carcinomatous cysts; no signal was identified in the nonneoplastic biliary elements. This indicates that cystadenocarcinomas have a mixed biological phenotype and suggests they could arise either from pluripotent cells or from neoplastic cells that reacquire epigenetic features. Our results suggest two possible diagnostic applications for albumin ISH: on routine sections, it could represent an important tool for distinguishing between cystadenoma and cystadenocarcinoma; and on fine needle biopsy specimens, it could reduce uncertainty between FNH and HA.