An oncogene is a type of gene that has the potential to cause cancer when it is mutated or expressed at high levels. Normally, these genes help regulate cell growth and division, but when they become altered, they can lead to uncontrolled cell proliferation. This can result in the formation of tumors and the spread of cancer in the body. Oncogenes are often derived from normal genes called proto-oncogenes, which play essential roles in normal cellular functions. Various factors, such as viruses, radiation, and chemical exposure, can trigger mutations in these genes, contributing to the development of different types of cancer.