CLDN4 and papillary serous cystadenocarcinoma: Furthermore, previous studies also indicated that the expression of CLDN4 could be utilized to distinguish the metastatic epithelial neoplasms in serous effusions and mesothelioma, including those from lung, breast, gastrointestinal tract, pancreas, ovary and primary serous papillary carcinoma of peritoneum.59, 60