Primary Peritoneal Low-grade Serous Carcinoma in a Patient With Lynch Syndrome: A Case Report.

Lynch syndrome (LS) is an autosomal dominant disease caused by a germline mutation in DNA mismatch repair genes which increases the risk of several cancers such as endometrial and colorectal cancers. However, there are only a few reports of peritoneal malignancies in patients with LS. Herein, we report the first case of a primary peritoneal low-grade serous carcinoma in a woman with LS and provide a literature review of peritoneal malignancies in patients with LS. The patient was a 72-yr-old gravid 2 para 2 Japanese woman with a germline mutation in MLH1. She had a history of colon cancer and endometrial cancer and was treated with total hysterectomy and bilateral salpingo-oophorectomy 14 yr ago. During the follow-up, peritoneal nodules were detected by abdominal computed tomography which were surgically resected. Pathologic examination revealed a low-grade serous carcinoma with cells positive for BerEP4, MOC31, CEA, and WT-1 and negative for BAP1, PAX8, MLH1, and PMS2, by immunohistochemistry. This case report and literature review show that peritoneal low-grade serous carcinoma can occur in patients with LS and that LS-related cancers usually precede primary peritoneal malignancies. The differential diagnosis for peritoneal nodules in patients with LS should, therefore, include peritoneal serous carcinoma and malignant mesothelioma besides metastasis of LS-related cancers. Considering the ambiguous immunophenotypes, a combination of immunohistologic markers would be useful for an accurate diagnosis of such cases.