POU5F1 and lung adenocarcinoma: 3.2. Immunofluorescence Staining Showed Co-Expression of OCT4 and c-MYC with NANOG, SOX2 and KLF4 by Tumor Gland Cells, and Exclusive Expression of OCT4 and c-MYC by Stromal Cells in Lung Adenocarcinoma Tissues