MUC4 is upregulated in ovarian carcinoma effusions and differentiates carcinoma cells from mesothelial cells

Using gene expression arrays, we recently showed that MUC4 expression is significantly higher in ovarian/primary peritoneal serous carcinoma (OC/PPC) compared to diffuse peritoneal malignant mesothelioma (DMPM). In the present study, we analyzed the anatomic site-related expression of MUC4 in OC/PPC and studied its prognostic role. We additionally studied the ability of MUC4 to differentiate between OC/PPC and reactive mesothelial cells (RMC). OC/PPC effusions (n = 142) and benign reactive effusions (n = 10) were immunostained for MUC4 expression. Immunoreactivity was scored in carcinoma cells and RMC and was compared with tumor cell expression in 60 previously studied primary carcinomas and solid metastases and analyzed for association with clinicopathologic parameters, including survival. MUC4 was detected in carcinoma cells in 141/142 (99%) effusions, with comparable expression in peritoneal and pleural effusions. RMC were present in 72 malignant effusions and were MUC4-negative in all specimens, as well as in the 10 reactive effusions. MUC4 expression in carcinoma cells in effusions was significantly higher than in primary carcinomas and solid metastases (P < 0.001). Higher MUC4 expression was seen in tumors from older (>60 year) patients (P = 0.049). No association was found between MUC4 expression and other clinicopathologic parameters, including survival. MUC4 is universally expressed in OC/PPC effusions and is upregulated at this anatomic site compared to primary carcinomas and solid metastases. The data in the present study, together with our earlier report, show that MUC4 is an excellent marker for differentiating OCIPPC from both benign and malignant mesothelial cells.