Duodenal Neuroendocrine Tumor Presenting as Iron Deficiency Anemia in an Older Adult.

Duodenal neuroendocrine tumors are rare neoplasms that are most often identified incidentally during endoscopic evaluation. They typically follow an indolent course. In older adults, iron deficiency anemia is a common finding that can present with symptoms such as fatigue, dyspnea, and weakness. This warrants thorough evaluation to exclude gastrointestinal sources, including less common malignancies. We report a 70-year-old man with a past medical history of prostate cancer treated with prostatectomy and hypertension who presented with fatigue and decreased exercise tolerance and was found to have iron deficiency anemia. Upper endoscopy revealed segmental mucosal abnormalities in the duodenum, including congestion, erythema, friability, granularity, nodularity, punctate white spots, and altered mucosal texture. Biopsies demonstrated a well-differentiated, grade 1 neuroendocrine tumor with adjacent benign villous mucosa and features of acute and chronic duodenitis with superficial erosion. Immunohistochemistry showed synaptophysin positivity and chromogranin negativity, with a low mitotic index, suggestive of a neuroendocrine tumor. This case highlights an unusual presentation of a rare malignancy in a duodenal neuroendocrine tumor identified during evaluation of iron deficiency anemia. It emphasizes the importance of comprehensive endoscopic assessment and targeted biopsy in patients with unexplained anemia, including consideration of uncommon gastrointestinal neoplasms.