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. TSGs are inactivated by mutations that destroy the function of the protein encoded by the gene, or by silencing of the gene's promoter. The biological behaviour of cancer can be considered in terms of eight specific hallmarks and two additional so-called enabling characteristics. Improved understanding of the mechanistic basis of these processes has revolutionized diagnosis, treatment and prognostication in cancer medicine.