Familial Cancer Syndromes

Key Terms: Gene, Inherited, Mutation.

Definition

Familial cancer syndrome is a genetic condition that causes an increased risk for specific types of cancers. Familial cancer syndromes account for only 5–10% of all cancers.

Description

Most cancer is not inherited. Cancer is common; in 2004, more than 1.3 million new cancer cases were diagnosed. Many people have relatives who have had cancer, but most of the time this is due to chance or environmental factors. In a familial cancer syndrome, an inherited genetic mutation causes a person to be at increased risk for cancer and other physical symptoms. There are many different familial cancer syndromes, and each one has a specific set of characteristic cancers and physical symptoms associated with it. For example, BRCA1 and BRCA2 gene mutations are associated with an increased risk for breast and ovarian cancer. Examples of other familial cancer syndromes include von Hippel-Lindau syndrome, Peutz-Jeghers syndrome, and Li-Fraumeni syndrome.

Features

Below is a list of "clues" in a family tree that make a familial cancer syndrome more suspicious:

• Two or more close relatives with the same type of cancer (on the same side of the family).
• Cancer diagnosed at an earlier age than usual.
• Cancer diagnosed more than once in the same person (more than one primary cancer, not a cancer recurrence).
• Cluster of cancers associated with a known familial cancer syndrome (such as breast and ovarian).
• Many cases of cancer in a family, more than can be accounted for by chance.
• Cancer in a person who also has birth defects.
• Evidence of autosomal dominant inheritance, which is when a gene from one parent overrides that of the other parent. When one parent has a dominant abnormal gene, offspring each have a 50% chance of inheriting that gene.

Diagnosis

The most important step in determining if a family has a familial cancer syndrome is gathering an accurate family history. The family history should include children, brothers and sisters, parents, aunts, uncles, grandparents, nieces, nephews, and cousins on both sides of the family. For a person who has had cancer, the type of cancer and age at diagnosis should be listed for each cancer. It may be necessary to obtain medical records to confirm what type of cancer a person had since family members may not always be aware of specific information. Birth defects, unusual skin findings, benign tumors, and special screening tests (such as colonoscopy to look for colon polyps) should also be noted. When this type of family information is unavailable, it may be possible to look for clues in one or a small number of family members. Many hospitals have a "familial cancer clinic," which is a team of health professionals with expertise in familial cancer syndromes. Geneticists, genetic counselors, oncologists, and social workers assist individuals and families by providing risk assessment, support, screening and prevention recommendations, and genetic testing options (if available).

Inheritance

Some familial cancer syndromes show autosomal dominant inheritance, which means that an affected person has a 50% chance of passing on the genetic mutation to each of his or her children. Other familial cancer syndromes show autosomal recessive inheritance, which means that both parents are usually not affected, but are carriers of a mutation for the condition. In autosomal recessive inheritance, each child born to parents who are carriers has a 25% chance of having the condition. When a person is diagnosed with a familial cancer syndrome, relatives should be examined for signs of the syndrome. Sometimes a person identified as having a familial cancer syndrome is the first person in the family to be affected. That person is able to pass the condition on to his or her children, but the parents and siblings are not affected. Depending on the syndrome, genetics professionals can determine who in the family is at risk.

Risks

Different familial cancer syndromes have different risks for cancer and associated symptoms. In general, a person who inherits the syndrome has a higher risk of developing the cancer associated with the syndrome than the general population, but this is not a guarantee that cancer will ever develop. On the other hand, someone who does not inherit the syndrome is not at increased risk for cancer above that of the general population, but this is no guarantee that cancer will not develop, and screening guidelines for the general population should be followed.

Genetic Testing

Although genetic testing is available for many familial cancer syndromes, there are genes that have yet to be discovered. Each syndrome has special issues surrounding genetic testing; for example, what age should the test be done? How would the results change medical management? Does insurance cover the test? How will the information affect the family? Health professionals familiar with familial cancer syndromes keep up to date with advances in cancer genetics, and work with families to discuss the risks, benefits and limitations of genetic testing.

The Human Genome Project

Since mid-2002, when the first complete draft of the Human Genome Project was completed, rapid advances have been made in the discovery of specific locations of cancer genes. For example, late in 2003, scientists tracked down the exact chromosome that carries certain familial forms of colorectal cancer. By mapping every normal gene in the human body, scientists can compare abnormal DNA sequences that lead to cancer. For example, the BRAF mutation has been linked to several cancers. Data from the Human Genome Project will help identify cancer genes, develop better genetic tests for cancer, and lead to improved preventive and therapeutic interventions.

Resources

Periodicals

Cummings, S. "The Genetic Testing Process: How Much Counseling Is Needed?" Journal of Clinical Oncology 18, Supplement (November 1, 2000): 60–4.

Elsas, L. J., and A. Trepanier. "Cancer genetics in primary care: When is genetic screening an option and when is it the standard of care?" Postgraduate Medicine 107 (April 2000): 191–208.

"Identifying Cancer Genes —Will it Really Lead to Better Treatment?" Biotech Week October 15, 2003: 645.

Lynch, H., et al. "Clinical Impact of Molecular Genetic Diagnosis, Genetic Counseling, and Management of Hereditary Cancer: Part I: Studies of Cancer in Families." Cancer 86 (1999): 2449–56.

Wiesner, Georgia L., et al. "A Subset of Familial Colorectal Neoplasia Kindreds Linked to Chromosome 9q22.2.–31.2." Proceedings of the National Academy of Sciences of the United States 100 (October 28,2003): 12961.

Other

"Autosomal Dominant Genes." WebMD June 2001. [cited June 27, 2001]. .

"Statistics." American Cancer Society. June 2001. [cited June 27, 2001]. .

—Laura L. Stein, M.S., C.G.C; Teresa G. Odle