Immunohistochemistry can help distinguish metastatic pancreatic adenocarcinomas from bile duct adenomas and hamartomas of the liver.

Not uncommonly, bile duct adenomas (BDAs) and hamartomas (BDHs) of the liver may be difficult to distinguish from metastatic well-differentiated ductal adenocarcinoma of the pancreas. However, this distinction is critical for proper staging and patient management. The primary purpose of this study was to determine if a panel of immunohistochemical stains can help distinguish BDA or BDH from metastatic pancreatic adenocarcinoma in the liver. Routinely processed tissue sections from 25 BDA, 10 BDH, 25 metastatic pancreatic adenocarcinomas to the liver and 6 cases each of metastatic colorectal, breast, and lung adenocarcinomas were immunohistochemically stained for CK7, CK8/CK18, CK19, CK20, p53, p63, TAG-72, monoclonal CEA (mCEA), polyclonal CEA (pCEA), HER-2/neu, AMACR (alpha-methylacyl-CoA racemase), Dpc4 (Smad4), and mesothelin. The slides were evaluated in a blinded fashion, and the results were compared between the benign and malignant lesions. Significantly more (P < 0.05) metastatic pancreatic adenocarcinomas were positive for CK20 (76%), p53 (60%), TAG-72 (88%), mCEA (92%), HER2/neu (40%), and mesothelin (64%) and showed loss of Dpc4 (44%), in comparison to BDA (CK20, 40%; p53, 0%; TAG-72, 0%; mCEA, 0%; HER2/neu, 12%; mesothelin, 0%; loss of Dpc4, 0%) or BDH (CK20, 10%; p53, 0%; TAG-72, 0%; mCEA, 10%; HER2/neu, 0%; mesothelin, 0%; loss of Dpc4, 0%). Of these antibodies, p53, TAG-72, mCEA, loss of Dpc4, and mesothelin had the highest specificity for pancreatic adenocarcinoma, with mCEA having the highest sensitivity (92%). No significant differences were observed in the degree of CK7, CK8/CK18, CK19, or pCEA expression between the three types of lesions. Although none of the BDA or BDH was positive for either p63 or AMACR, two of the metastatic pancreatic adenocarcinomas (8%) were positive for each of these peptides (P > 0.05). For nonpancreatic adenocarcinomas, mCEA showed a reasonably high sensitivity and 100% specificity in the differential diagnosis versus BDA. Immunohistochemical expression of p53, TAG-72, mCEA, mesothelin, and loss of Dpc4 can help distinguish metastatic pancreatic adenocarcinoma in the liver from BDA or BDH. Although p63 and AMACR are also specific for pancreatic adenocarcinoma, their low sensitivity limits their use in clinical practice.