Early Liver Metastasis from Early Gastric Adenocarcinoma with a Small Neuroendocrine Carcinoma Component: A Case Report.

Introduction: Gastric neuroendocrine carcinoma (NEC) is a rare histological subtype of gastric malignancy. A small NEC component may coexist with gastric adenocarcinoma, making preoperative diagnosis challenging. Currently, no established treatment strategies exist for cases in which an NEC component is identified only in postoperative pathological findings.

Case presentation: An 82-year-old man underwent esophagogastroduodenoscopy during a routine health checkup and was diagnosed with early-stage gastric cancer. The lesion was a superficial tumor, 30 mm in diameter, located on the lesser curvature of the cardia. Biopsy revealed well-differentiated adenocarcinoma. The patient subsequently underwent laparoscopic proximal gastrectomy with D1+ lymph node dissection. Histopathological examination of the resected specimen revealed adenocarcinoma with an NEC component, accounting for approximately 10% of the tumor. The pathological stage was T1bN1M0 (Stage IB), and the patient did not receive adjuvant chemotherapy. Five months after the surgery, the patient developed anorexia and weight loss. CT revealed multiple liver tumors. Diagnostic laparoscopy with excisional biopsy of the liver lesion was performed, revealing no peritoneal dissemination. Histopathological examination confirmed that the liver tumors were metastatic NEC, indicating hepatic recurrence of gastric NEC. Given the patient's rapidly deteriorating condition and a performance status of 3-4, aggressive chemotherapy was deemed inappropriate, and palliative care was initiated. The patient died of the primary disease 8 months after surgery.

Conclusions: A small NEC component may be undetectable preoperatively. The prognosis of mixed tumors is dictated by the malignancy of the NEC component rather than its tumor burden. Therefore, clinicians should consider NEC-equivalent adjuvant chemotherapy and intensive surveillance.