Inhibin expression in ovarian-type stroma in mucinous cystic neoplasms of the pancreas.

Mucinous cystic neoplasms (MCNs) of the pancreas are typically found in middle-aged to elderly women and contain ovarian-type stroma in the cyst wall. Whether the resemblance of this stroma to ovarian stroma is only morphologic or has more functional similarity is still unclear. Estrogen receptors (ER) and progesterone receptors (PR) have been shown to be expressed in a wide variety of tissues and tumors, including the ovarian-type stroma of MCN. Inhibin, on the other hand, has been shown to have a more restricted expression, limited to ovarian sex cord-stromal components and placental cells, and has recently been shown to be expressed in pancreatic MCNs. However, it is still unclear whether this expression is limited to MCNs of the pancreas and whether it has any diagnostic role. Seven cases of MCN (4 mucinous cystadenoma, 2 borderline MCN, and 1 mucinous cystadenocarcinoma with microinvasion), 6 cases of intraductal papillary mucinous tumor, 1 of mucinous cystic tumor of uncertain classification, 2 of mucinous noncystic adenocarcinoma, 4 of serous cystadenoma, and 4 solid pseudopapillary neoplasms were selected for this study. Five cases with normal pancreatic tissue were included as controls. Immunohistochemical stains for alpha-inhibin, ER, and PR were performed on a representative section from each case on formalin-fixed, paraffin-embedded tissue sections using a standard indirect immunoperoxidase method. All cases of MCN were in female patients with an average age of 55.3 years, showing ovarian-type stroma and clusters of alpha-inhibin-positive luteinized theca-like cells. In all these cases, moderate to strong PR positivity was also noted in the ovarian-type stroma, including many of the alpha-inhibin-positive luteinized theca-like cells. ER was expressed in 2 cases. The epithelial cells of MCNs were all negative for ER, PR, and alpha-inhibin staining. Of the other tumors, 4 solid pseudopapillary neoplasms showed positivity for only PR in the tumor cells. The remaining tumors were negative for all markers. In conclusion, the finding of alpha-inhibin positivity in MCN with ovarian-type stroma further supports its similarity to true ovarian stromal tissue and may suggest a role of complex hormonal interaction in the pathogenesis. In addition, its limited expression in MCNs of the pancreas may be diagnostically useful in difficult cases.