Cancer is a common disease which affects about 1 in 3 people at some point in their lifetime. For most individuals it is a disease of old age and occurs by chance. For some time it has been recognised that certain rare forms of cancer, such as retinoblastoma, are caused by an inherited predisposition. An inherited predisposition means that there is a gene fault which can be passed from one generation to the next.
It is only within the last few years that progress has been made in understanding the role that inherited gene faults play in determining a proportion of the more common cancers, such as breast, ovarian, colorectal and other cancer syndromes.
Most cancer 90%-95% is sporadic and occurs by chance. It is likely that only 5%-10% of the disease occurs because of an inherited predisposition or gene faults. These inherited gene faults, though comparatively rare, give rise to a high lifetime risk of developing cancer. In families where there is an inherited predisposition cancer tends to occur at a younger age, the same type of cancer may affect several family members, there may be unusual cancers or two different cancers may affect one family member.
It is thought that a further 10%-20% of breast, colorectal and ovarian cancers may be caused by other inherited "medium risk" gene faults which can also give rise to significant increased risk