Based on these phenomena, in order to further investigate the relationship of EGFR signaling and EGFR endocytosis, we have now used confocal immunofluorescence microscopy to substantiate the detailed mechanisms for endocytosis of the ligand-induced activated form of EGFR, i.e., phosphorylated EGFR (pEGFR), via the early endosome/late endosome/lysosome endocytic pathway in both NSCLC cell lines, namely, the PC9 and QG56 cell lines. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.