Early Detection and Curative Endoscopic Submucosal Dissection of a 4-mm Signet Ring Cell Microcarcinoma in a Reconstructed Gastric Tube: A Case Report.

Gastric tube cancers are rare but clinically challenging entities that may arise years after esophageal or gastric surgery. Due to anatomical alteration and subtle mucosal changes, early detection remains difficult, particularly for signet-ring cell carcinoma (SRCC), which often progresses unnoticed. We report a rare case of micro SRCC arising in a reconstructed gastric tube, which was detected early and curatively resected by endoscopic submucosal dissection (ESD). The patient was initially diagnosed with adenocarcinoma of the esophagogastric junction during a routine esophagogastroduodenoscopy (EGD) performed as part of a medical check-up at a local clinic. He underwent ESD, but the pathological evaluation revealed a positive vertical margin, and he was subsequently referred to a tertiary center. Curative resection was achieved through open proximal gastrectomy combined with robot-assisted thoracoscopic esophagectomy of the middle and lower esophagus. Two years postoperatively, a follow-up EGD revealed a small, flat, whitish lesion measuring 5 mm on the lesser curvature of the gastric angle in the reconstructed gastric tube. Biopsy results revealed undifferentiated-type gastric cancer, predominantly composed of SRCC. Given the lesion's clearly shallow invasion and very small size on endoscopic examination, ESD was performed. Pathological findings confirmed a 4 × 4 mm SRCC limited to the mucosal layer, with negative horizontal and vertical margins, and no lymphovascular invasion, consistent with curative resection. This case highlights the importance of vigilant long-term endoscopic follow-up after upper gastrointestinal surgery and demonstrates that even micro SRCCs in reconstructed gastric tubes can be successfully detected and treated at an early stage by ESD.