Oncogenes and Cancer

There are several different causes of cancer, all of which boil down to genetic mutations of some sort. It's how the mutations arise that make the difference. Some are inherited, some arise from exposure to chemicals or radiation and some occur spontaneously, as mutations do, during replication, but are not repaired properly. An oncogene is any gene that participates in the progression of cancer, by promoting the transition of normal cells to cancerous cells. The gene product of an oncogene might not normally be expressed, or is expressed at low levels, but somehow expression is triggered or amplified and that leads to uncontrolled replication of cells. An oncogene might be the mutated form of a proto-oncogene, causing accelerated cell proliferation once mutated, or it might be a gene, transcription of which is under the control of another oncogene. Some oncogenes are activated by viruses (e.g. a factor in cervical cancer). Cancer-promoting genes might be those involved in cell signaling cascades such as ras and myc, or those that encode transcription factors. Other oncogenes might exert their effect by preventing apoptosis (normal cell death), or failing to do their job as tumor-suppressor genes, which inhibit cell division.