Gastric Regional Lymph Node Metastases from a Squamous Cell Carcinoma of Unknown Primary Site: A Case Report

A cancer of unknown primary site is a malignant tumor for which the primary site is unknown despite a thorough examination, and which has been histologically proven to be a metastatic lesion. Metastases to intraperitoneal and to gastric regional lymph nodes are rare.

A 75-year-old woman was diagnosed with a gastric submucosal tumor with infiltration to other organs. Endoscopic ultrasound-guided fine needle aspiration revealed cells that appeared to be derived from epithelial tissue, but a definitive diagnosis could not be obtained. Because the possibility of gastric cancer could not be ruled out, an open proximal gastrectomy with systematic lymph node dissection and combined resection of other organs were performed. A grade II pancreatic fistula developed, but resolved with conservative treatment, and the patient was discharged 15 days after surgery. Histopathologically, the tumor was a lymph node metastasis consisting of squamous cell carcinoma cells that had grown primarily outside the gastric wall, but involved the gastric wall and pancreas and protruded into the gastric mucosa. Thirty-five gastric lymph nodes were dissected, and metastases were found in five of them. Primary squamous cell carcinoma of the stomach and pancreas was ruled out. Because no head and neck, esophageal, or pulmonary lesions that could be squamous cell carcinoma were identified, the primary tumor could not be identified. The diagnosis was a gastric regional lymph node metastasis of a cancer of unknown primary site protruding into the gastric wall. Nivolumab was initiated after surgery, and the patient has remained alive and free of recurrence 7 months after surgery.

In cases of metastases originating from a cancer of unknown primary site to lymph nodes in the gastric region, the removal of the affected lymph nodes followed by inability to detect the primary lesion might be considered to be equivalent to an R0 resection.