P40 and TTF-1 double-expressing non-small cell lung cancer with EML4-ALK and PIK3CA gene mutations: A case report and review of the literature.

P40 and thyroid transcription factor-1 (TTF-1) dual expression in non-small cell lung cancer (NSCLC) is a rare occurrence. However, the presence of EML4-ALK and PIK3CA gene mutations in this type of cancer is unknown. The present study describes the case of a 38-year-old male patient who had never smoked. A 4.5-cm mass adjacent to his right upper mediastinum was detected by a computed tomography (CT) scan of the chest. Biopsy of the level four lymph nodes in the right mediastinum revealed microscopic morphological features typical of high-grade NSCLC. Immunohistochemical findings resembled those reported previously for several cases of NSCLC with the dual expression of P40 and TTF-1 markers. In addition, echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit a (PIK3CA) gene mutations were detected using high-throughput next-generation sequencing. To the best of our knowledge, this is the first report of NSCLC with the expression of P40 and TTF-1 as well as EML4-ALK and PIK3CA gene mutations. The presence of this type of tumor should be considered in patients with NSCLC who have never smoked and may have unique clinicopathological features.