Immunohistochemistry for the differentiation of peritoneal disseminated carcinoma of unknown origin

We report a woman with ascites, hydrothorax, pancreatic tumor, left cystic ovarian tumor, and an elevated serum cancer antigen 125 level. Exploratory laparotomy was performed to determine peritoneal disseminated carcinoma of unknown origin. Immunohistochemical analysis demonstrated positive staining for carcinoembryonic antigen, trypsin, and progesterone receptor and nonspecific or negative reaction for calretinin, estrogen receptor, amylase, lipase, Wilms tumor gene 1 protein, and inhibin or chromogranin A. These results together with the morphology of tubular structure suggested the pathological diagnosis of adenocarcinoma with pancreatic characteristics and contradicted ovarian cancer or mesothelioma. Immunohistochemistry is an adjunct tool to differentiate the primary site of carcinomatous peritonitis.