KRT7 and lung adenocarcinoma: The representative images of the immunostaining for usual PAC, primary PEAC and CRAC were shown in Fig. 2 (usual PAC: TTF-1+, CDX2−; primary PEAC: CK7+, CDX2+; CRAC: TTF-1−, CDX2+; TTF-1 was chosen because of its better specificity than CK7 in the diagnosis for lung adenocarcinoma).