A Rare Case of Gastric Neuroendocrine Tumor in a Patient With Vitamin B12 Deficiency.

Vitamin B12 deficiency can result from gastric neuroendocrine tumors (GNETs), which are uncommon neoplasms frequently linked to hypergastrinemia and chronic atrophic gastritis. Here, we report the case of a 48-year-old vegetarian male from South India who presented with jaundice, fatigue, and gastrointestinal discomfort. He was diagnosed with macrocytic anemia, mild hepatomegaly, and significant vitamin B12 deficiency. An incidental upper gastrointestinal endoscopy revealed multiple gastric nodules, later confirmed as a well-differentiated GNET. The patient also had a high hepatitis B viral load. He was treated with vitamin B12 supplementation and underwent resection of the tumor followed by antiviral therapy for hepatitis B. Postoperative recovery was uneventful with improvements in anemia and liver function. This case emphasizes the importance of a multidisciplinary approach and thorough evaluation when addressing patients with vitamin B12 insufficiency, hepatitis B, and GNET.