While each of the majority of tumor specimens can be subtyped alone by examination of typical morphological features on common hematoxylin/eosin-stained histological sections [7], identification of immunohistochemical markers, mainly the combinations of TTF1 and CK7 for lung adenocarcinoma and p40/p63 and CK5/6 for lung squamous cell carcinoma, is also necessary to provide an accurate pathological diagnosis, especially a precise subclassification of poorly differentiated NSCLC with a high degree of cell pleomorphism, for personalized medicine [7,8,9,10]. The gene discussed is TTF1; the disease is lung adenocarcinoma.