Genes and cancer

Abstract

Cancer can be considered a genetic disorder of somatic cells. Strong evidence comes from several areas: (1) chromosomal analysis reveals cancer cells have abnormal karyotypes; (2) some inherited syndromes are associated with an increased risk of cancer and for others, cancer itself occurs as an inherited trait; (3) cells can become malignant by a variety of agents that damage DNA, and (4) some types of viruses can induce tumours. One common thread has been the normal cellular sequences transduced by viruses and mutated to become oncogenic (oncogenes) are the same sequences to become activated by nonviral mechanisms. These oncogenes appear involved in cell proliferation and/or differentiation and their products apparently function in the signal transduction pathway from the cell exterior to the nucleus. In addition, evidence from familial studies indicate mutations associated with gene inactivation or loss of function are also important in the aetiology of tumour formation. These genes, termed tumour suppressor genes, seem to be involved in the negative control of cellular proliferation. Cancer is a multistep process and it is now becoming clear that the different stages involve genetic alterations in both oncogenes and tumour suppressor genes.