Biology of cancer

Cancer is caused by aberrant patterns of gene expression. In general, the genes affected 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. Germline mutations of tumour suppressor genes can account for rare hereditary cancer syndromes. The biological behaviour of cancer can be considered in terms of six specific hallmarks: growth factor independence, insensitivity to anti-growth signals, avoidance of apoptosis (programmed cell death), sustained angiogenesis, cellular immortalization, and tissue invasion and metastasis.