Background: Lung cancer, particularly small-cell lung carcinoma (SCLC), often presents with respiratory symptoms. However, atypical manifestations including jaundice and abdominal pain can obscure the diagnosis, leading to challenges in early detection and treatment. Case Presentation: A 49-year-old male, with a history of smoking and diagnosed with Chronic Obstructive Pulmonary Disease (COPD), presented to the emergency department with a 3-day history of jaundice and a 3-week duration of mild abdominal pain. Initial investigations, including blood tests, showed hyperbilirubinemia and elevated lipase and amylase levels. An abdominal ultrasound was performed and revealed a hypoechoic, inhomogeneous mass in the head of the pancreas and multiple liver masses, suggesting a cephalo-pancreatic formation with liver metastasis. Further diagnostic procedures, including upper endoscopy and ERCP, followed by a TAP CT scan, identified a large mediastinal-pulmonary mass with invasion into major vessels and extensive metastasis. The immunohistochemical analysis of a duodenal ulcer biopsy confirmed a diagnosis of duodenal metastasis from a small-cell neuroendocrine lung carcinoma. Conclusion: Our case highlights that while rare, the possibility of metastatic spread should be included in the differential diagnosis when obstructive jaundice occurs in the context of high-risk factors for lung cancer.