RB1 and lung cancer: Using reverse phase protein arrays (RPPAs) to analyze changes in cell signaling proteins in a high-throughput manner, we screened a panel of previously characterized isogenic murine epithelial-like and mesenchymal-like lung cancer cell lines and observed an increase in CDK4 axis–related molecules, phospho-RB and Cyclin D1, in cells with a mesenchymal phenotype (Figure 2C).