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A genetic counselor is a health professional with specialized education and experience in the areas of medical genetics and counseling. A genetic counselor works as a member of a health care team, providing information and support to individuals and families who are dealing with a genetic condition or who may be at risk for a variety of inherited conditions. At Billings Clinic, I provide genetic counseling primarily to patients in the obstetrics and oncology departments.

Most cancer, perhaps 90 percent to 95 percent, results from sporadic changes or damage to a cell. The damage, whether from sunlight, cigarette smoke or some other environmental exposure, affects the genetic material (DNA) in the cell. If any one cell accumulates excessive damage to the DNA, the cell may become cancerous. Therefore, all cancer is genetic, because it involves our genetic material that affects the body's ability to repair and reconstruct damaged DNA.

However, only a small portion of cancer is inherited. We all inherit DNA from our parents, with half of it coming from our mothers and half coming from our fathers. Our DNA is made up of many "regions," called genes, and we have two copies of each gene (one each from mom and dad). Most of the genes we inherit from our parents work normally, carrying on specific important jobs in our bodies. However, sometimes we can inherit changes or mutations to our genes. If we inherit a mutation to certain genes, we are at increased risk for developing cancer. These abnormal genes are called cancer predisposition genes.

Many cancer predisposition genes have been identified, and the cancer syndromes associated with mutations to these genes have been specified and described. The most common of these include hereditary breast and ovarian cancer syndrome, Lynch syndrome and familial adenomatous polyposis syndrome.

Hereditary breast and ovarian cancer syndrome is caused by mutations to the BRCA1 or BRCA2 genes (from breast cancer). The normal function of these two genes is to help repair damage to the DNA inside a cell. If either of these genes is not working correctly, DNA damage can accumulate, which increases the likelihood that the cell will become a cancer.

Women who have inherited a mutation to either the BRCA1 or BRCA2 genes have a greatly increased risk for developing breast and/or ovarian cancer. Men with an inherited BRCA1 gene mutation have an increased risk for developing prostate cancer, and men with a BRCA2 gene mutation have an increased risk for developing breast cancer.

Lynch syndrome is caused by inherited mutations in one of four known genes. These genes - MLH1, MSH2, MSH6 and PMS2 - are all normally involved in repairing DNA mismatch, a problem that happens as DNA is copied to make new cells. If an individual has an inherited mutation in one of these four genes, the new DNA that is produced often contains an error. If a sufficient number of errors accumulate in one cell, that cell can become cancerous. The cancers that are most often seen in families with Lynch syndrome include colon and uterine cancers. In some families, there is also an increased risk for developing cancers of the stomach and/or ovaries.

Familial adenomatous polyposis syndrome is caused by inherited mutations in the APC gene. The normal APC gene is thought to help control when cells divide and when they die. It is also possible that the APC gene helps with maintaining the stability of large "packages" of DNA, called chromosomes.

Inherited mutations in this gene might therefore allow damaged cells to divide, prevent damaged cells from dying off, or allow the chromosomes to become unstable. The most common finding in individuals with familial adenomatous polyposis syndrome is hundreds of polyps lining the colon. These polyps, if not removed, become cancerous. Therefore, individuals and families with mutations to the APC gene are at very high risk for developing colon cancer. Other cancers that can be associated with this syndrome include cancers of the stomach, small intestines and pancreas.

Families with inherited cancers can often be distinguished from families with sporadic cancers by looking closely at the family medical history. We typically find patterns in families with hereditary cancers. These include a family having more individuals with the same type of cancer than we would expect by chance, cancers occurring unusually early, individuals having more than one cancer, and a particular cancer in two or more generations. If a family fits this pattern, there is a greater chance that a mutation to one of the cancer predisposition genes runs in the family.

You may wonder why it is helpful to know if you are part of a hereditary cancer family. The primary benefit is to help you understand your personal risk for developing cancer.

If you know your risk is high, you might choose to have more frequent cancer screening, leading to early detection. Cancers detected early are most treatable. You could also consider treatment options, even before you develop cancer, which may reduce your cancer risk. And after all, the best treatment for cancer is the prevention.

Susan Landgren, MS, is a certified genetic counselor in the departments of Oncology and Obstetrics & Gynecology at Billings Clinic.