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CANCER, GENES AND INHERITED PREDISPOSITION OvERvIEw – Cancer Genetics

The second requirement is a clear and well defined starting point. For popu- lation-based cancer registries, the starting date (from which the survival is calculated) is the incidence date (see Section 17.3.1). The third requirement is a clear and well defined outcome. Death is gener- ally the outcome of interest, but some registries collect enough data to allow them to conduct analyses using recurrence of tumour, or first recurrence of a particular complication, as the outcome of interest. It is also necessary to formulate clear criteria for deciding who should be considered ‘lost to fol- low-up’. For instance, certain registries would assume that cases for which it was not. | FACT SHEET CANCER GENES AND INHERITED PREDISPOSITION OVERVIEW - Cancer Genetics 1 47 Produced by the Centre for Genetics Education. Internet http www.genetics.edu.au Important points A family history of cancer can occur - Just by chance because cancer is common - Because family members are exposed to the same environmental factors - Because a predisposition to cancer is running in the family though this is rare We all have in our cells two copies of a number of different genes that control orderly growth and division of our cells throughout life growth control genes When these growth control genes become faulty in cells in a particular part of the body eg breast tissue the cells divide and grow out of control and accumulate to form a cancer Cancer occurs as a result of uncontrolled cell division and growth. These growth control genes can therefore be thought of normally acting as cancer protection genes All cancers can be considered genetic in origin because they arise from changes in the normal cancer protection genes that we all have. A change in the information in a cancer protection gene that makes the gene faulty is called a mutation The cause of the changes that make the cancer protection gene faulty is unknown but may be due to a combination of genetic factors environmental factors and the process of ageing The development of cancer is not a quick or simple process. It is a progression involving a build-up of changes in a number of different cancer protection genes in the cells of the body tissues over a lifespan. This is why the development of cancer can take many many years and is more often seen in older people Most people are born having two working copies of each of the different cancer protection genes in their cells. This means that most people have not inherited a genetic predisposition to developing cancer A small number of people inherit from a parent a change in one of the copies of one of their cancer protection genes that make the gene copy .