An oncogene is a protein encoing gene, which — when deregulated — participates in the onset and development of cancer. Genetic mutations resulting in the activation of oncogenes increase the chance that a normal cell will develop into a tumor cell. Since the 1970s, dozens of oncogenes have been identified in cancer. Oncogenes are figuratively thought to be in a perpetual tug-of-war with tumor suppressor genes which act to prevent DNA damage and keep the cell's activities under control. There is much evidence to support the notion that loss of tumor suppressors or gain of oncogenes can lead to cancer.