ABSTRACT
Cancer is a common disease, affecting up to a third of the population at some time in their lives. All cancer can be termed ‘genetic’ as cancer is caused by genetic mutations (alterations in the DNA code), which result in abnormal cellular growth and/or proliferation. The majority of these mutations are sporadic (only occur in the cancer cell) and only a small proportion of these cases (approximately 5-10 per cent)1 are due to the inheritance of a germ-line mutation in a high-penetrance cancer pre-disposition gene. This mutation is then present in every somatic cell and, on average, in half the gametes (a gamete only contains half of the total genes) and therefore has a chance of being passed onto the offspring of an affected individual. These mutated cancer pre-disposition genes have a well-defined pattern of inheritance. Approximately a further 20 per cent of cancer cases can be described as familial, i.e., there is a clustering of cancer cases within the family, but they do not show a welldefined pattern of inheritance. These family clusters may be due to the chance clustering of common cancers, the inheritance of genes that are associated with only a slightly increased cancer risk, the sharing of common environmental influences, or they may be of multifactorial origin, possibly as a result of the inheritance of genes that render an individual more susceptible to environmental influences.
