Cancer cells are able to alter signaling pathways to sustain proliferation and growth. This is achieved by secreting growth factors, elevating growth factor receptor levels, altering receptors for ligand-independent signaling, activating signaling pathway proteins or inactivating negative feedback loops. Understanding the roles of genes and proteins in individual signaling pathways requires molecular tools, such as protein:protein interaction assays, reporter gene assays and CRISPR/Cas9 gene editing.