Glucagonoma is a rare neuroendocrine tumor arising from alpha cells of the pancreatic islets, producing pathological hypersecretion of glucagon that drives the characteristic 4D syndrome: Dermatitis (necrolytic migratory erythema), Diabetes, Deep vein thrombosis, and Depression. The dermatologic manifestation — necrolytic migratory erythema (NME) — is the presenting feature in approximately 70% of cases and results from glucagon-induced hypoaminoacidemia: excessive glucagon stimulates hepatic amino acid uptake for gluconeogenesis, depleting circulating amino acids essential for epidermal protein synthesis and cell turnover, producing the characteristic painful, erythematous patches with central clearing and peripheral blistering that migrate across the perineum, groin, and extremities. Diabetes mellitus results from glucagon's direct hepatic effects: activation of glycogen phosphorylase (glycogenolysis) and phosphoenolpyruvate carboxykinase (gluconeogenesis) via the cAMP-PKA pathway in hepatocytes, producing sustained hyperglycemia. The diabetes is typically mild because functioning beta cells compensate with increased insulin secretion, maintaining a relative balance. Venous thromboembolism occurs in approximately 30% of patients through glucagon-mediated upregulation of tissue factor and factor X activation, combined with the hypercoagulable state of malignancy. Most glucagonomas are solitary, located in the pancreatic body or tail, and...