Friday, June 17, 2011

Your genetic risk of cancer

St. Luke’s Health Watch

Dr. Martin B. Durtschi

Approximately 12 million Americans currently live with cancer. Every one of them developed cancer because of a genetic defect, but very few of them either inherited that gene from their parents or will pass it on to their children. Only about 5 to 10 percent of people with cancer inherited the responsible gene from their parents. All the remaining patients have what is called "sporadic" defects, meaning the defective gene occurred for the first time in one of their individual cells and will not be passed on to later generations.

Scientists estimate that there are between 20,000 and 25,000 genes in each of our bodies. These genes instruct each individual cell in how to replicate and function. Faulty instructions may result in a single cancerous cell.

Much of the time, the body's immune system recognizes those cells as abnormal and destroys them before they can grow into what we recognize as cancer. When the immune system either does not identify the abnormal cells or fails to kill them, a cancer may result.

Often a genetic defect may exist, but will need to interact with an external factor before a cancer can begin to grow. These factors may include hormones (either those produced by your own body or those from an external source), the environment, diet, exercise and even other genes.

Medicine is now concentrating on studying the cancer genes that we know can be passed from parent to child, so that we can identify individuals at high risk for cancer and screen them regularly. Regular screening results in early diagnosis and early diagnosis results in a very high cure rate. In the future, early identification of these genes may allow preventive treatment even before a cancer begins.

Common cancers, like those of the breast and colon, can occur from either inherited or sporadic genetic defects. For example, about 10 percent of women with breast cancer will have inherited the defective gene from a parent, while 90 percent of women will develop breast cancer only because of a defective gene in one of their cells. BRCA1 and BRCA2 are the most common inherited genes, but there are other, less commonly known defective genes that also dramatically increase the risk of breast cancer. If a woman has one of these genes, her chance of developing breast or ovarian cancer during her lifetime may be as high as 70 percent. By contrast, a woman without any of these genes has only about a 10 percent chance of developing either of those cancers.

Doctors may be suspicious that a person might have an inherited genetic defect, and therefore be at high risk for developing breast cancer, if she or he (yes, men can develop breast cancer, too) has two or more first-degree relatives—parent, sibling or child—with breast cancer, or with both breast and ovarian cancer. People also are considered at high risk if they have more than one first-degree relative with two or more different types of cancers. Ashkenazi Jewish background also is associated with an increased chance of having a genetic predisposition for breast cancer.

Once someone has been identified as at risk for an inherited gene defect, genetic counseling and testing can be done. This is usually a blood test and St. Luke's Wood River can arrange for it, although most of the tests are sent to a few national specialty laboratories. However, before such testing is done, a visit with your physician is mandatory, since a vital part of screening for genetic abnormalities or early cancers is a careful history and physical examination.

For example, any patient who is at risk for colon cancer will need a colonoscopy, and a woman will need a mammogram or a magnetic resonance imaging. Many patients who might be concerned about their genetic status can be reassured by a physician visit and spared the expense and inconvenience of screening.

There are many other cancers, both common and rare, that have an inherited genetic basis, and researchers continue to investigate the very complex interactions that determine whether an individual actually develops cancer. But even as we understand more each day, it is apparent that there is no replacement for good health habits and careful screening with you doctor.

Dr. Martin Durtschi is board certified in general surgery. He is a graduate of the University of Washington School of Medicine in Seattle.

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