Genetic Testing for Hereditary Cancers

When cancer develops in more than one member of a family, it often prompts such comments as “Cancer must run in that family.” But because cancer is common, it can develop in several members of a family purely by chance rather than through an inherited abnormal gene (a genetic mutation). In fact, only about 5 percent to 10 percent of cancers are strongly linked to inherited genetic mutations.

Overview

Advances in technology now make it possible for many families to learn whether cancer is actually the result of a genetic mutation. This knowledge can help you and your doctor make informed decisions about how to detect cancer at its earliest stages, treat cancer most effectively or lower your chances of ever getting cancer. 

The cancers with known hereditary links and available genetic tests include cancers of the breast, ovaries, colon, uterus and skin (melanoma). It is important to note that cancer does not develop in every individual who has a cancer-related genetic mutation.

An inherited genetic mutation does not automatically cause cancer, but it does substantially increase an individual’s chance of developing cancer, being diagnosed at a younger age and being diagnosed with cancer more than once. The increased risk for cancer varies according to which gene has a mutation (see Table 2).

Inheritance of Genetic Mutations

Every individual has two copies of each gene at birth — one copy inherited from your mother and one from your father. You can have an inherited cancer syndrome if one of a pair of cancer-related genes contains a genetic mutation, usually passed down from one parent. If you have a genetic mutation, you have a one in two (50 percent) chance of passing it to your children because you can pass along a copy of the normal gene or a copy of the gene with a mutation.

Definitions of Hereditary Syndromes

Abnormalities in the BRCA1 and BRCA2 (breast cancer 1 and breast cancer 2) genes were among the first cancer-related gene mutations to be identified. Mutations in either of these genes increase the risk for breast and ovarian cancer (see Table 2 on page 41). Thus, this hereditary cancer is referred to as hereditary breast and ovarian cancer syndrome. The risk of certain other cancers may also be higher in people with this cancer syndrome.

There are several forms of hereditary colorectal cancer. The most common form is hereditary nonpolyposis colorectal cancer (or Lynch syndrome). This hereditary cancer syndrome is also associated with an increased risk of uterine and ovarian cancer as well as upper-gastrointestinal tract cancers and cancer of the urinary tract and kidney. Other types of hereditary colorectal cancer syndromes are associated with multiple polyps that grow in the colon.

The most common of these polyposis syndromes include familial adenomatous polyposis (FAP), attenuated FAP (AFAP), and MYH-associated polyposis (MAP). In FAP, hundreds to thousands of polyps develop in the colon over a lifetime, and they can start developing as early as childhood. In AFAP, fewer than 100 polyps usually develop. In MAP, the number of polyps that develops ranges from a few polyps to thousands. Additional polyposis syndromes exist, and your doctor may suggest that you be tested for these syndromes, depending on the number and type of polyps seen on colonoscopy.

A genetic mutation has also been linked to melanoma. Hereditary melanoma is not as well understood as the other hereditary cancer syndromes, and researchers continue to learn more about the genetic mutations that may be responsible for this hereditary cancer. Hereditary melanoma is also associated with an increased risk for pancreatic cancer

Genetic Testing and Counseling

Genetic testing is done to determine if a person has an inherited genetic mutation. Because inherited cancers account for only a small percentage of cancers, genetic testing is not right for everyone. About one in five women with breast and/or ovarian cancer and one in four individuals with colorectal cancer are candidates for genetic evaluation and possible genetic testing. Because the mutations involved with hereditary melanoma are not well known, genetic testing for this type of cancer is generally reserved for patients involved in clinical studies.

Any decision about whether to have genetic testing depends on your personal and family medical history. Several red flags are strong indicators that you should talk to your doctor about genetic testing (see Table 1). Genetic testing itself is easy and convenient; a blood sample is drawn and analyzed for evidence of a particular genetic mutation.

If you undergo genetic testing, you should receive genetic counseling at the same time. Genetic counselors identify which genes should be tested, help you better understand your risk for cancer, explain how genetic testing will affect you and your family and tell you what options are available to reduce the risk of cancer if a genetic mutation is found. A doctor or other health-care provider must order genetic counseling and testing. Thus, if you are concerned about your risk of cancer, you should talk to your doctor about any family history of cancer and the potential benefits of genetic testing.

If you are found to have a genetic mutation, your doctor will strongly encourage you to share the test results with your family members because there is a 50 percent chance of a mutation in a first-degree relative (a sibling, child or parent). Except for conditions that cause childhood cancer, genetic testing is not done on young children; instead, testing is done when children have reached adulthood, are old enough to understand the implications of testing and are at an age when they need to consider screening. For example, it is usually recommended that testing for BRCA1 and BRCA2 mutations not occur until a woman is in her early 20s.

When genetic testing is appropriate, it offers several important benefits. If you have been diagnosed with cancer, the identification of an inherited mutation may lead you to decide to have more extensive surgical treatment to help prevent the risk of a second cancer. But regardless of whether you have been diagnosed with cancer, cancer screening should be done more frequently, and it should be done at an early age, when a genetic mutation is found.

For example, individuals who inherit the genetic mutation for Lynch syndrome should have a screening colonoscopy every one to two years beginning at age 20 to 25. Colonoscopy done at short intervals allows for polyps to be removed before they become cancerous, and it dramatically reduces the risk of colorectal cancer. More frequent cancer screening also means that cancer can be found earlier; the earlier cancer is detected, the higher the chance for cure. Negative test results regarding a known familial mutation are also a benefit because knowing that there is no genetic mutation can relieve stress and lessen the need for frequent follow-up care and cancer screening.

People used to be concerned about discrimination if they were identified as being at risk for cancer. In May 2008, President George Bush signed the Genetic Information Nondiscrimination Act (GINA) into law, making it illegal to discriminate on matters of employment and health insurance based on genetic information. The Health Insurance Portability and Accountability Act (HIPAA) and certain state laws also protect the confidentiality of individuals’ health information and help protect against employment discrimination.

Genetic testing can be expensive, and the cost depends on several factors, including the complexity of the test and how many family members are tested. The initial testing is usually the most expensive, but once a mutation is identified in a particular family, the cost drops significantly for relatives who subsequently undergo testing. In most cases, Medicare and private health insurance cover testing, but individuals who are considering testing may want to learn about their insurance coverage first. Some testing laboratories are able to help individuals verify their insurance coverage prior to starting testing.

If you decide to have genetic testing, you should remember that it cannot identify all possible causes of hereditary cancer. In addition, a negative test result does not eliminate the possibility that cancer will develop. Regardless of the results of genetic testing, following appropriate prevention and screening guidelines is the most important way to help reduce the risk of cancer

Charts and Tables

Table 1. Red Flags for the Possibility of Hereditary Cancer

Several factors may be red flags indicating the likelihood of hereditary cancer. If you answer 'yes' to any of the questions associated with these red flags, you should talk to your health-care provider about genetic testing for hereditary cancer.

Red Flag Question to Ask Yourself
Early age at time of cancer diagnosis Was I diagnosed with cancer before the age of 50?
Multiple cancers in one individual Have I been diagnosed with more than one primary cancer?
Multiple family members with the same type of cancer Do I have more than one family member who has been diagnosed with the same type or related types of cancer? (Examples of related types of cancer are breast and ovarian cancer, colorectal and endometrial cancer, and melanoma and pancreatic cancer.)
Identification of gene mutation in family member Do I have a family member who has been found to have a gene mutation associated with hereditary cancer?

 

Table 2. Risks of Cancer in Hereditary Cancer Syndromes and Possible Reasons for Genetic Testing

  Breast and Ovarian Cancer Colorectal Cancer/ Endometrial Cancer
(HNPC C/Lynch Syndrome)
Colorectal Cancer/ Adenomatousa Polyposis Syndromes Melanoma
Risk of cancerb if appropriate screening and/or prevention methods are not utilized
Female breast cancer: 56 percent to 87 percent
 
Male breast cancer: about 6 percent
 
Ovarian cancer: 27 percent to 44 percent
Colorectal cancer: 20 percent to 82 percent*
 
 
Endometrial cancer: 15 percent to 60 percent*
 
Ovarian cancer: about 12 percent*
 
 
*risk depends on gene involved
80 percent to 100 percent 53 percent
 
Possible reasons to perform genetic testing 
Personal or family history of
 
• Breast cancer before age 50 (or male breast cancer at any age)
 
• Ovarian cancer at any age
 
• Two breast cancers or breast and ovarian cancer in any one family member
 
Ashkenazi or Eastern European Jewish heritage
Personal or family history of colorectal or endometrial cancer before age 50
 
Personal history of two primary colorectal cancers or colorectal cancer and endometrial cancer, regardless of age
 
Two or more Lynch syndrome cancers diagnosed in close family members, regardless of age
Personal or family history of multiple colorectal polyps (more than 15 polyps in a lifetime)
Two or more melanomas in an individual or family
 
Melanoma and pancreatic cancer in an individual or family
 
Relative who carries the gene mutation
 
Other cancers associated with the inherited mutation
Cancer of the pancreas, prostate, stomach, melanoma
Cancer of the stomach, pancreas, kidney/urinary tract, brain, sebaceous skin tumors
Cancer of the small bowel, thyroid, pancreas, brain
Pancreatic Cancer

a) The adenomatous polyposis syndromes are familial adenomatous polyposis (FAP), attenuated FAP (AFAP) and MYH-associated polyposis (MAP).

b) The risk of cancer for individuals with a genetic mutation is given as the risk up to age 70, with the exception of the risk for individuals with hereditary melanoma, which is given as the risk by age 80.

HNPCC = hereditary nonpolyposis colorectal cancer

 



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