Biphasic gastric adeno-choriocarcinoma in a patient with known lynch syndrome – A case report

Abstract

Primary gastric choriocarcinoma is a rare aggressive tumour accounting for less than 0.1% of all cases of gastric cancer. The majority of reported cases possess an adenocarcinoma component. Here we report a 46-year-old woman with known Lynch syndrome with MLH1 germline mutation, and a history of descending colon mucinous adenocarcinoma at age 39 presenting with a gastric tumour with multiple liver metastases and a solitary lung metastasis. Serum beta-hCG and CEA were markedly elevated at 185,000 U/L and 101.7 μg/L, respectively. Biopsy of the tumour showed a poorly differentiated biphasic carcinoma comprising 50% adenocarcinoma and 50% choriocarcinoma components. Adenocarcinoma was positive for CK7, CDX2, and Villin, whereas choriocarcinoma was positive for CK7, hCG, and p40. Interestingly, whilst the choriocarcinoma component showed loss of MLH1 and PMS2, the adenocarcinoma component showed normal mismatch repair protein immunohistochemistry. The patient subsequently underwent palliative radiation therapy. To the best of our knowledge, this is the first case of Lynch syndrome associated gastric cancer with an unequivocal choriocarcinoma component. The differential pattern of mismatch repair protein expression suggests early clonal separation of cancer progenitor cells during tumorigenesis.