At the molecule level, individual cancers are driven by their own sets of dysregulated protein-protein interactions. Due to the lack of PCR technique for proteins, these protein-protein interactions cannot be amplified. Single-molecule detection could thus be unique, ideal route for characterizing these ¡®inherently heterogeneous and tiny¡¯ protein-protein interactions. I will talk about an antibody-based, label-free method that characterizes the signaling dynamics of native proteins. We have used our technique to characterize two core oncoproteins, KRas and EGFR in different samples including cancer cell lines, xenograft tumors, cancer-patient biopsy samples. We have characterized the single-molecule signaling kinetics and the proportion of single proteins that are actively binding with the downstream proteins tagged with fluorescent proteins. We also compare our analysis results, which are at the protein-protein interaction level, with the genotyping results of samples, which is the current standard for personalized medicine. Our results demonstrate the possibility that the single-molecule techniques could be a real analysis tool for clinically important samples, beyond cutting-edge tool for the curiosity-based science.