Combination of MUC5ac and WT-1 Immunohistochemistry is Useful in Distinguishing Pancreatic Ductal Carcinoma from Ovarian Serous Carcinoma in Effusion Cytology

Malignant ascites may be the first presentation of an unsuspected cancer. Pancreas and ovary are among the organs that are usually evaluated as a source of primary. The purpose of this study is to investigate a panel of immunohistochemical stains to help differentiate pancreatic from ovarian carcinoma. We evaluated the immunohistochemical staining of eight commercially available antibodies MUC1, MUC2, MUC5ac, Wilm's tumor susceptibility gene 1 (WT1), cytokeratin 7 (CK7), CK20, CA125, and CA19.9 in 25 effusion specimens with evidence of metastatic carcinoma including 14 ovarian serous carcinomas, 9 pancreatic adenocarcinomas, and 2 unknown primaries. Primary ovarian serous carcinomas were positive for WT-1 (100%), CK7 (93%), CK20 (43%), CA125 (100%), CA19.9 (50%), MUC1 (100%), MUC2 (0%), and MUC5ac (0%). Primary pancreatic carcinomas were positive for MUC5ac (100%), MUC1 (100%), CA19.9 (100%), CK7 (78%), CK20 (22%), CA125 (89%), WT-1 (0%), and MUC 2 (0%). The combination of MUC5ac positivity/WT-1 negativity was seen in 100% of pancreatic carcinoma, whereas MUC5ac negativity/WT-1 positivity in 100% of ovarian serous carcinoma. It appears that the combination of MUC5ac and WT-1 stains is useful in distinguishing pancreatic ductal from ovarian serous carcinoma in body fluid cytology.