S6440 A Case of Gastrocolic Fistula Turning Out to Be Gastric Adenocarcinoma

Introduction: The development of a fistula between segments of the gastrointestinal tract is a rare occurrence in malignant disease. Gastrocolic fistula (GCF) can be caused by both benign and malignant conditions. Malignant gastrocolic fistula is most associated with adenocarcinoma of the transverse colon. Gastric adenocarcinoma causing a fistulous opening into the colon is rare. Case Description/Methods: An 80-year-old woman presented following a motor vehicle accident. Review of systems revealed a 1-month history of dark stools, nausea, vomiting, diarrhea, and a 10-pound weight loss over the past year. Initial labs revealed severe anemia (Hb 4.4 g/dL). Computed tomography (CT) abdomen demonstrated a large, circumferential, deeply ulcerated mass in the gastric antrum and pylorus with a direct fistulous communication to the adjacent transverse colon. Tumor markers were elevated (carcinoembryonic antigen 307.6 ng/mL, CA 19-9: 50 U/mL). Esophagogastroduodenoscopy revealed a large ulcerated fistulous opening between the stomach and colon. The endoscope was easily advanced through the fistula into the colon. Diffuse ulceration was seen on both the gastric and colonic sides. Biopsies from the lesion showed poorly differentiated adenocarcinoma with signet-ring features, favoring a gastric origin. Pancreaticobiliary origin could not be completely excluded. Given the patient’s advanced age and frailty, she was deemed not a candidate for curative treatment and was transitioned to hospice care. Discussion: This case illustrates a rare presentation of GCF resulting from advanced gastric adenocarcinoma. Classic symptoms such as weight loss, feculent vomiting, and diarrhea may be absent, complicating early recognition. Imaging and endoscopy are critical in identifying fistulous tracts and obtaining tissue for diagnosis. The presence of signet-ring features portends a poor prognosis. Surgical resection remains the standard treatment; however, many patients present with advanced disease precluding curative options. This case highlights the importance of early suspicion, multidisciplinary evaluation, and individualized management in complex gastrointestinal malignancies.