What are proto-oncogenes and how do they differ from oncogenes?

Proto-oncogenes are normal genes that play a role in cell growth and division. They can become oncogenes through mutations, which cause them to promote excessive cell growth and division, leading to cancer. The main difference between proto-oncogenes and oncogenes is that proto-oncogenes are normal, whereas oncogenes have undergone mutations that make them cancer-causing genes.