Cancer Causes :Genetics and Cancer

Heredity and Cancer

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. This can be caused by a number of factors. Often, family members have certain risk factors in common, such as smoking, which can cause many types of cancer. 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 are inherited. 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 also can affect your chance of getting certain diseases, such as cancer.

An abnormal change in a gene is called a mutation. The 2 types of mutations are inherited and acquired. Inherited gene mutations are passed from parent to child through the egg or sperm. These mutations are in every cell in the body. But most mutations that occur are not present in the egg or sperm. These mutations are called somatic. Somatic mutations are acquired at some point in the person's life. This type of mutation occurs in one cell, and then is passed on to any new cells that are the offspring of that cell.

Genes are found on chromosomes. Humans have 23 pairs of chromosomes in each cell. We inherit one set of chromosomes from each parent. Each chromosome can contain hundreds or thousands of genes that are passed from the parents to the child. 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.

Genes and cancer

Genes seem to have 2 major roles in cancer. Some, called oncogenes, can cause cancer. Others, known as tumor suppressor genes, stop cancer from developing or growing.

Oncogenes are mutated forms of certain normal genes of the cell called proto-oncogenes. Proto-oncogenes are often genes that normally control what kind of cell it is and how often it grows and divides. When a proto-oncogene mutates (changes) into an oncogene, it turns on or activates when it is not supposed to be. When this occurs, the cell can grow out of control, leading to cancer.

Tumor suppressor genes are normal genes that slow down cell division, repair DNA mistakes, and 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.

A tumor suppressor gene is like the brake pedal on a car. It normally keeps the cell from dividing too quickly just as a brake keeps a car from going too fast. When something goes wrong with the gene, such as a mutation, cell division can get out of control.

An important difference between oncogenes and tumor suppressor genes is that oncogenes result from the activation (turning on) of proto-oncogenes, but tumor suppressor genes cause cancer when they are inactivated (turned off).

Even if you were born with healthy genes, some of them can become changed (mutated) over the course of your life. These mutations are known as sporadic or somatic, meaning they are not inherited. Sporadic mutations cause most cases of cancer. These mutations are thought to be caused by things that we are exposed to in our environment, including cigarette smoke, radiation, hormones, and diet. More gene mutations build up as we get older, leading to a higher risk of cancer.

When someone has inherited an abnormal copy of a gene, their cells already start out with one mutation. This makes it all the easier (and quicker) for enough mutations to build up for a cell to become cancer. That is why cancers that are inherited tend to occur earlier in life than cancers of the same type that are not inherited.

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