Causes of cancer linked to family

Family Cancer Syndromes

Cancer is such a common disease that it is no surprise that many families have at least a few members who have had cancer. Sometimes, certain types of cancer seem to run in some families. Sometimes, this is because family members have certain risk factors in common, such as smoking, which can cause many types of cancer. It can also be due in part to other factors, like obesity, that tend to run in families and influence cancer risk.

But in some cases the cancer is caused by an abnormal gene that is being passed along from generation to generation. Although this is often referred to as inherited cancer, what is inherited is the abnormal gene that can lead to cancer, not the cancer itself. Only about 5% to 10% of all cancers result directly from gene defects (called mutations) inherited from a parent. This document focuses on those cancers. 

DNA, genes, and chromosomes

Cancer is a disease of abnormal gene function. Genes are pieces of DNA (deoxyribonucleic acid). They contain the instructions on how to make the proteins the body needs to function, when to destroy damaged cells, and how to keep the cells in balance. Your genes control things such as hair color, eye color, and height. They can also affect your chance of getting certain diseases, such as cancer.

Every cell in your body has all of the genes you were born with. Although all cells have the same genes and chromosomes, different cells (or types of cells) may use different genes. For example, muscle cells use a different set of genes than skin cells use. The genes that the cell doesn't need are turned off and not used. The genes that the cell is using are activated or turned on. 

An abnormal change in a gene is called a mutation. The 2 types of mutations are inherited and acquired (somatic).

• An inherited gene mutation is present in the egg or sperm that formed the child. After the egg is fertilized by the sperm, it created one cell called a zygote that then divided to create a fetus (which became a baby). Since all the cells in the body came from this first cell, this kind of mutation are in every cell in the body (including eggs or sperm) and so can be passed on to the next generation.
• An acquired (somatic) mutation is not present in the zygote, but is acquired some time later. It occurs in one cell, and then is passed on to any new cells that are the offspring of that cell. This kind of mutation is not present in the egg or sperm, and so cannot be passed on to the next generation. Somatic mutations are much more common than inherited mutations. Most cancers are caused by acquired mutations.

You have 2 copies of most genes – one from each parent. When someone has inherited an abnormal copy of a gene, their cells already start out with one mutation. If the other copy of the gene stops working (because of an acquired mutation, for example), the gene can stop functioning altogether. When the gene that stops working is a cancer susceptibility gene, cancer can develop. Some cancer susceptibility genes function as tumor suppressor genes. 

Tumor suppressor genes are normal genes that slow down cell division, repair DNA mistakes, or tell cells when to die (a process known as apoptosis or programmed cell death). When tumor suppressor genes don’t work properly, cells can grow out of control, which can lead to cancer. Many family cancer syndromes are caused by inherited defects of tumor suppressor genes.

Someone who isn’t born with a bad copy of a gene would have to acquire 2 different mutations for that gene not to work. Acquiring 2 mutations in the same gene takes longer than acquiring one, which is why cancers that are caused by inherited gene mutations tend to occur earlier in life than cancers of the same type that are not.

More information about gene changes that can lead to cancer can be found in our document Genes and Cancer.

 

 

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