Occult gastric carcinoma with microsatellite instability diagnosed 10 years after excision of metastatic lymph node: a case report.

Background: Suprapancreatic lymph node metastasis is one of the usual routes for gastric cancer. However, it is rare for the primary lesion to be found several years after resection of the suprapancreatic metastatic lymph node. This is a report of occult gastric carcinoma with microsatellite instability diagnosed 10 years after excision of a metastatic lymph node.

Case presentation: A 55-year-old female presented with suprapancreatic lymph node swelling during a medical examination. Gastroscopy revealed no malignancy. We performed an excisional biopsy via laparotomy and histologically suspected metastatic cancer of unknown origin. After nine and a half years, we detected early gastric cancer by gastroscopy and performed a distal gastrectomy. The gastric tumor was pathologically similar to the previous suprapancreatic tumor. Immunohistochemical examination revealed that both the stomach and suprapancreatic lymph node exhibited microsatellite instability, suggesting that the two lesions were of the same origin.

Conclusions: This case is considered valuable because there have been no previous reports of gastric cancer with characteristics of high microsatellite instability in which the primary tumor was identified a long time after resection of metastatic lesions.