What is the role of tumour suppressor genes and oncogenes in the development of tumours?

Think of tumour suppressor genes and oncogenes like the pedals used to operate a car. Oncogenes are mutated forms of proto-oncogenes. Normally, these proto-oncogenes act like the gas pedal, and allow the cell to get to the next stage of the cell cycle. I.e. they stimulate cellular replication (S phase) or segregation (mitosis). Examples of these genes include Res and Myc. In cancerous cells, these genes are mutated to oncogenes; and have increased activity leading to uncontrolled cell division and tumour development. In contrast, tumour suppressor genes act like the brake pedal. They prevent cellular growth and division, and can promote apoptosis (programmed cell death). Examples of these genes include p53 and RB1. In cancerous cells, mutations in these genes prevent them from working effectively, stopping them from inhibiting cell proliferation and leading to uncontrolled cell division and tumour development. So, although mutations in tumour supressor genes and oncogenes can both lead to uncontrolled cell proliferation and tumour development, the two occur through different methods.