Biology of cancer

Cancer is caused by aberrant patterns of gene expression. Most common cancers are caused by acquired mutations in somatic cells. In contrast, specific germline mutations can account for rare hereditary cancer syndromes. In general, the genes affected in cancers can be divided into two groups: oncogenes and tumour suppressor genes. Oncogenes undergo activation and are phenotypically dominant, while tumour suppressor genes undergo inactivation and are phenotypically recessive. Oncogenic activation can occur by specific point mutations within the sequence of a gene, by amplification of the number of copies of the gene or by translocation of DNA to a site where transcription is more active or where the formation of a new fusion gene generates a protein with enhanced biological activity. Tumour suppressor genes are inactivated by mutations that destroy the function of the protein encoded by the gene. 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 resulted in rapid progress in diagnosis, treatment and prognostication in cancer medicine.