Low-grade serous primary peritoneal carcinoma incidentally found in a hernia sac

Very rarely, a primary peritoneal serous carcinoma can be observed in a hernia sac. We herein describe a low-grade serous primary peritoneal carcinoma incidentally found in a postmenopausal woman following examination of the femoral hernia repair sac. Our case is significant for its unusual presentation. The lesion initially appeared as a 0.3-cm tumor that disseminated in the peritoneum, persisted, and progressed for 75 months. The absence of ovarian disease indicated a primary peritoneal origin. Tumor cells were immunohistochemically positive for PAX8, claudin-4, and VE1, excluding the possibility of being of mesothelial origin. Recognition that a low-grade serous primary peritoneal carcinoma can be incidentally found in a hernia sac should simplify future diagnoses. Immunohistochemistry is helpful in making the correct diagnosis.