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Genetic Testing for Colon Cancer

Cancer and genes

The ancient greeks could not have imagined genetic testing for colon cancer. They believed that cancer was caused by too much body fluid. They called this fluid "black bile." Doctors in the 17th and 18th centuries suggested that parasites caused cancer.

Researchers are working hard to understand more about how genes work inside the body and why things sometimes go wrong. Recently, cancer research has focused on understanding how a normal cell, through a series of genetic changes, turns into a cancerous cell. We hope this brief discussion helps you understand why researchers think genetic testing for colon cancer can save lives.

How genes cause cancer

For various reasons, genes often undergo mutations (changes). Some mutations have no effect on a cell, while other mutations are harmful or helpful to the cell.

There are two types of genetic changes or mutations:

  • those that are passed down from parent to child
  • those that happen during the lifetime of a person and are not passed on to the next generation

If the mutation is passed from one of the parents to the child, it is called a germline mutation. When a germline mutation is passed on from a parent to the child, it is present in every cell of the child's body, including the reproductive sperm and egg cells. Because the mutation affects reproductive cells, it is passed from generation to generation. Germline mutations are responsible for 5% to 10% of cancer cases. This is also called familial (occurring in families) cancer.

Most cancers are caused by a series of mutations that develop during a person's lifetime called acquired mutations. Acquired mutations are caused by tobacco, over-exposure to UV radiation, and other toxins and chemicals. These mutations are not in every cell of the body and are not passed from parent to child. Cancer caused by this type of mutation is also called sporadic cancer.

Most scientists believe that cancer happens when several genes of a particular group of cells become mutated. This makes genetic testing for colon cancer very difficult because not all the genes always test positive for mutations. Some people may have more inherited mutations than others, and even with the same amount of environmental exposure, some people are simply more likely to develop cancer and we don’t know why. Lots of research is devoted to finding out why.

Inheriting risk

In most cases, people who inherit a known cancer gene will not definitely get cancer. Inheriting a cancer gene usually means you have a greatly increased risk of developing cancer compared to other people in the population. So you don't really inherit cancer from your family, but you might inherit an increased risk of developing cancer. This is why genetic testing for colon cancer could be valuable to your health. This type of increased risk is sometimes also called a predisposition or susceptibility.

It is important to remember that everyone has a certain risk of developing cancer in their lives, whether they have people in their family with cancer or not. This risk increases with age, which means that old people are far more likely to develop cancer than young people. It is relatively rare for young people to get cancer. This is true even if a person has one close relative with cancer. Close relatives are parents, children, brothers, sisters, aunts, uncles and grandparents.

Can cancer genes 'skip' a generation?

Not everyone who inherits a cancer susceptibility gene actually gets cancer. Sometimes it looks as if cancer skips a generation in families in which many members have cancer. But on a genetic level, you either inherit the gene from one of your parents or you don't. There is a 50/50 chance. If you don't inherit the gene, you can't pass it on to your children. So the genetic mutation cannot skip a generation. However, not everyone with the mutation will necessarily develop cancer, so it can seem that the cancer skipped one generation.

Does colon cancer run in families?

Most people who develop colon cancer don't have a strong history of it in their family. The greatest single risk for developing colon cancer is getting older. Other risk factors for colon cancers include lifestyle factors such as diet and exercise.

But there are some families with a strong history of colon cancer. This means having:

  • Parent, brother, sister, son or daughter who developed colon cancer below the age of 45, or
  • Two or more first degree relatives on the same side of the family with colon cancer at any age

Some types of colon cancer that run in families also can cause an increase in other types of cancers, such as:

  • cancers of the womb
  • stomach
  • pancreas
  • ovary
  • kidney

Anyone can have an inherited risk of cancer in your family if they have a relative with colon cancer and relatives on the same side of the family with these other cancers.

Some families have more people in the family with colon cancer than you would expect by chance but no specific gene fault is found. The greater number of cancers in these families may be due to shared environmental factors (such as diet) but may also be due to an inherited gene which has not been discovered.

Is there a colon cancer gene?

So far, three types of inherited gene changes which increase the risk of colon cancer have been found. These are:

  • Familial adenomatous polyposis (FAP)
  • Hereditary non polyposis colorectal cancer (HNPCC)
  • MYH associated polyposis or MAP

It is possible that other genes will be identified in the future.

How can a person know if he or she has inherited a genetic mutation that increases his or her risk of colorectal cancer?

Only genetic testing for colon cancer can determine whether you have a genetic mutation. Most experts strongly recommend that people considering genetic testing first consult a genetic counselor. Genetic counselors are trained to explain the risks and benefits of genetic testing.

Protect Yourself From the High Cost of Cancer

According to the recent studies, American men have a 44% chance of developing cancer while the chances for women are about 37%. The general risk of developing colon cancer in the United States is about 6%. For this reason, it's important for everyone, particularly people above the age of 50 years, to go for routine screening.

Whether discovered early or late, cancer is a debilitating disease due to the care, costs and the mental and physical trauma involved. Many times the cost of treatment leaves the patient in heavy financial distress.

Most insurance plans do not cover the total cost of the treatment, which leaves the patient and their family in a lurch. These days people have started purchasing supplemental cancer insurance that can help in covering otherwise uninsured expenses related to cancer illness.

Written by Deborah Theres - 2/24/09

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