Synchronous endometrial and ovarian cancer in Lynch syndrome with a MSH2 germline mutation: A case report.

Synchronous endometrial and ovarian cancer (SEOC) is a rare entity among gynecological cancers, which exhibits endometrioid histology in its early stages and generally has a good prognosis. However, diagnosis is difficult and recent reports have demonstrated that most clinically diagnosed cases of SEOC have clonally related cancers, indicating metastatic cancer. The association of SEOC with Lynch syndrome is also not clearly understood. We herein present the case of a 41-year-old SEOC patient with MSH2 mutation. The endometrial cancer was an endometrioid adenocarcinoma and the ovarian cancer was mainly endometrioid, but also included a clear cell carcinoma with a borderline clear cell adenofibromatous component, indicating primary ovarian cancer. Both tumors exhibited microsatellite instability (MSI) and loss of expression of MSH2 and MSH6. The patient had a family history of colorectal and gastric cancers. Genetic analysis revealed a germline mutation in exon 6 of MSH2 (c.1042C>T, p.Gln348*) and the patient was diagnosed with Lynch syndrome. This MSH2 mutation has only been registered in one case in the InSiGHT variant databases and has not been reported in a gynecological tumor or SEOC to date. This case is a rare example of a patient with genetically diagnosed Lynch syndrome who also developed SEOC. This synchronous cancer is not common, but it may be caused by Lynch syndrome. Testing for MSI and immunohistochemistry for mismatch repair deficiency is necessary in cases with suspected SEOC.