KRT20 and neoplasm: Immunohistochemical staining showed that the tumor cells were positive for thyroid transcription factor‐1 (TTF‐1; Figure 3b) and keratin 7 (K7; Figure 3c) but negative for keratin 20 (K20; Figure 3d) and prostate‐specific antigen (Figure not shown), which supported the diagnosis of poorly differentiated lung adenocarcinoma (Figure 3b–d).