Annexin A10 is an immunohistochemical marker for adenocarcinoma of the upper gastrointestinal tract and pancreatobiliary system.

AIMS: Annexin A10 (ANXA10) is a calcium- and phospholipid-binding protein expressed normally in the gastric mucosa. In this study, we evaluated the potential use of ANXA10 as a diagnostic marker.

METHODS AND RESULTS: We observed ANXA10 expression in the gastric mucosa, the Brunner gland of the duodenum and the urothelium, but absence of expression in other normal organs. Following the screening of 1327 primary carcinomas of major organs, we identified ANXA10 expression in 46% of gastric, 72% of ampullary, 78% of pancreatic and 33% of biliary adenocarcinomas. ANXA10 was expressed in 83% of non-invasive urothelial carcinomas, but was expressed in only 9% of invasive urothelial carcinomas. ANAX10 was rarely expressed in carcinomas of other organs. Of 227 metastatic adenocarcinomas, ANXA10 was expressed in 83% of metastatic pancreatic and 47% of metastatic gastric adenocarcinomas, but was expressed in only 2% of metastatic adenocarcinomas from other organs. In the liver, the sensitivity and specificity for identifying the pancreas as the primary site of metastatic adenocarcinoma were 83 and 95%, respectively.

CONCLUSION: Our study results indicate that the inclusion of ANXA10 in an immunohistochemical panel will be helpful in the differential diagnosis of adenocarcinoma of an unknown primary site.