Some cases of high-grade neuroendocrine carcinoma of the lung harboring mutations have been sporadically reported.<h4>Methods</h4>We describe the case of a 78-year-old woman with large-cell neuroendocrine carcinoma of the lung, with mutation in exon 21 L858R and co-expression of adenocarcinoma markers.<h4>Results</h4>A mass (3.0 cm in diameter) was identified in the inferior lobe of the left lung, accompanied by metastases into ipsilateral mediastinal lymph nodes and elevations of serum pro-gastrin-releasing peptide and carcinoembryonic antigen. The gene discussed is CEACAM5; the disease is pulmonary large cell neuroendocrine carcinoma.