The biology of cancer

Cancer is a genetic disease. Most common cancers are caused by acquired mutations in somatic cells. In contrast, specific germline mutations account for rare hereditary cancer syndromes. In general, cancer-associated genes can be divided into two groups: oncogenes and tumour suppressor genes (TSGs). Oncogenes undergo activation and are phenotypically dominant, while TSGs undergo inactivation and are phenotypically recessive. Oncogenic activation can occur by: specific point mutations within the gene sequence; amplification of the number of copies of the gene; or translocation of DNA to sites where transcription is more active or where a new fusion gene is formed that encodes a protein with enhanced biological activity.