Pulmonary large cell neuroendocrine carcinoma (LCNEC) is an uncommon type of non-small cell lung cancer (NSCLC) with an incidence of approximately 3% of all lung cancer diagnoses. The patient was a 60-year-old male with a 90-pack year smoking history who presented with dyspnea on exertion and productive cough for five weeks. Decreased breath sounds without respiratory distress and generalized cachexia were noted on the initial physical exam. Laboratory results were unremarkable except for chronic microcytic anemia. Computed tomography revealed extensive lymphadenopathy of the paratracheal, paraaortic, hilar, and nodes surrounding the left pulmonary arteries. Additionally, there were areas of necrosis in the left upper lobe, lingula, and left lower lobe with extensive pleural thickening extending to the abdomen and subcutaneous tissue of the anterior chest wall. Biopsy and staining showed disorganized tight cell clusters with irregular and prominent nuclei and numerous lymphocytes consistent with LCNEC. Immunohistochemistry was positive for neural cell adhesion molecule CD56 and synaptophysin, which was indicative of neuroendocrine origin. It was also positive for pan-cytokeratin antibody AE1 and AE3 and cytokeratin (CAM) 5.2, which arise from epithelial origin consistent with NSCLCs. Lastly, the patient's tissue was positive for thyroid transcription factor-1, which confirmed the tumor's primary lung origin. This combination of neuroendocrine and primary lung tumor markers, in conjunction with the histology, confirmed the patient's diagnosis of LCNEC.