Neuroendocrine Tumor of Unknown Origin Leading to the Diagnosis of Advanced Celiac Disease: A Case Report Exploring a Possible Association

Introduction: Celiac disease (CD), if left untreated, can predispose a wide range of intestinal malignancies including enteric lymphoma and adenocarcinoma. On rare occasions, intestinal neuroendocrine tumors (NETs) were reported. We present a case of metastatic NET that led to the diagnosis of CD. Case Presentation: A 58-year-old woman presented with a lump in the left axilla without fever or weight loss. Physical examination showed a single tender and rubbery lymph node (LN) of 2.5cm in size in the left axilla. Labs showed mild iron-deficiency anemia. An excisional LN biopsy showed well-differentiated NET, grade 3. A gallium Ga-68 DOTATATE integrated positron emission tomography-computed tomography scan (PET/CT) scan showed non-specific homogenous duodenal and small bowel uptake without apparent signs of fluorodeoxyglucose (FDG)-avid malignancy. Upper endoscopy with push enteroscopy with small bowel biopsies were consistent with CD. The serum tissue transglutaminase-immunoglobulin test was positive. The patient was started on a gluten-free diet and managed with clinical observation. A follow-up FDG-PET scan after six months showed no abnormal uptake, and the patient continued to be asymptomatic beyond one year of follow-up. Conclusion: This case highlights the possible rare coexistence of celiac disease with an atypical neoplastic process, particularly in patients presenting with unexplained iron-deficiency anemia. While celiac disease is associated with an increased risk of certain rare gastrointestinal malignancies, its relationship with neuroendocrine tumors remains poorly defined. Larger studies are needed to further explore any potential association between celiac disease and neuroendocrine tumors.