Endometrioid endometrial cancer “recurring” as high-grade serous adenocarcinoma in the inguinal lymph nodes in a patient with germline MLH1 mutated Lynch syndrome: consequence or coincidence?

BACKGROUND: Inguinal metastasis of endometrial cancer (EC) is rare. The aims of the study were to identify whether the inguinal metastatic tumor was originated from EC and to present the management of the disease. METHODS: The clinical data of a case of endometrioid EC “recurring” as serous adenocarcinoma in the inguinal lymph nodes were collected and analyzed. Paired samples of primary and metastatic tumors were used for exome sequencing to determine whether the tumors are same origination and to identify potential gene mutations associated with the relapse. RESULTS: The patient presented with right inguinal lymphadenopathy and histopathology revealed metastatic serous adenocarcinoma. A germline MLH1 mutation was identified. A combination of bioinformatical methods and cancer-related gene exome sequencing assay identified that only 17 (0.1%) somatic gene mutations were shared by the primary EC and the metastatic inguinal tumor, suggesting that the metastasis did not originate from the primary EC. Postoperative radiation therapy followed by a combination of chemotherapy were performed. Thirty-four months after that, the patient was doing well without any evidence of recurrence. CONCLUSIONS: This is the first case of metastatic inguinal serous adenocarcinoma in a woman with Lynch syndrome shortly after surgical treatment of stage I endometrioid EC. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13053-019-0112-x) contains supplementary material, which is available to authorized users.