Some cancers develop as a result of genetic factors that occur in families. These cancers are linked to abnormal changes (mutations) in genes that are passed from generation to generation. People with these mutations have a higher chance of developing certain types of cancer.
Just because a person has a relative who had cancer, it does not mean that cancer is hereditary. About 5 percent to 10 percent of all cancers are considered hereditary. Only a small proportion of some of the most common types of cancer – such as colon and breast cancer – occur as a result of genetic factors.
Families may have hereditary cancer if there are multiple people in the family with cancer, including more than one generation of family members with the disease. In addition, people diagnosed at a young age are more likely to have hereditary cancer. Some genetic mutations are more common among certain ethnic groups.
People with a strong family history of cancer may want to consider undergoing clinical genetics assessment with a genetic counselor and genetics physician. These professionals typically help patients document their family medical history and collect available medical records of family members with cancer. If a cancer risk appears to be hereditary, they may recommend genetic testing to identify specific gene alterations, typically performed using a blood sample.
Even if an individual is found to carry an altered gene, genetic testing cannot determine if cancer is present or when it may develop. It can only confirm an inherited tendency for the disease. However, genetic tests can help people make some medical decisions, such as determining the best plan for cancer screening or whether to pursue preventive therapy.
Who should consider cancer risk assessment and genetic counseling?
The following groups of people may want to consider cancer risk assessment, according to Siteman Cancer Center’s hereditary cancer program:
- Any person with a family history of cancer who is interested in learning more about his or her family-based cancer risk
- Any person who has a family member with hereditary cancer or who has a gene mutation
- Any person who is considering prophylactic medical or surgical therapy because of his or her family history of cancer
- Any person who was diagnosed with cancer early in adulthood
- Any person who is interested in learning more about genetic testing for cancer.
Information about some hereditary cancer syndromes
There are many different hereditary cancer syndromes, some of which are listed below. For families with hereditary cancer, the word syndrome refers to risk for different cancer types due to the same gene mutation.
The specific name does not indicate all of the cancer types family members may be at risk to develop. For example, families with some of the hereditary breast cancer syndromes also may have an increased risk of developing ovarian cancer. Knowing the different cancers associated with each hereditary cancer syndrome allows family members to undergo earlier and more frequent cancer screening.
Breast-ovarian cancer syndrome 1 results from an abnormal change in the BRCA1 gene. Female family members have an estimated 80 percent lifetime chance of developing breast cancer and a 40 percent to 60 percent lifetime chance of developing ovarian cancer. Mammography and breast magnetic resonance imaging (MRI) screening as well as ovarian cancer screening are recommended for female family members with a gene alteration.
Breast-ovarian cancer syndrome 2 results from an abnormal change in the BRCA2 gene. Female family members have an 80 percent lifetime chance of developing breast cancer and a 20 percent lifetime chance for ovarian cancer. Other cancers are associated with this syndrome, including melanoma and pancreatic, prostate and gastric cancers. Mammography and breast magnetic resonance imaging (MRI) screening as well as ovarian cancer screening are recommended for female family members with a gene alteration.
Familial adenomatous polyposis is a type of hereditary colon cancer that results from an abnormal alteration in the APC gene. Individuals develop hundreds to thousands of abnormal growths (polyps) in the colon. Since any of the polyps may develop into cancer, removal of the colon is recommended. Polyps may develop in other areas of the digestive system, requiring lifelong cancer screening.
Familial melanoma results from an abnormal alteration in at least one of three genes. Families with familial melanoma have an increased chance of developing melanoma and may have an increased chance for pancreatic and brain tumors. Monthly skin self-exams and clinical examinations by a dermatologist every six months are recommended.
Lynch syndrome (hereditary nonpolyposis colorectal cancer) is a hereditary colon cancer syndrome resulting from an abnormal change in one of at least five genes. Family members with lynch syndrome have an 80 percent lifetime risk of developing colon cancer. Female family members have a 40 percent to 60 percent lifetime risk of developing endometrial/uterine cancer. Other cancers, such as gastric or kidney tumors, may be associated with this syndrome. Colon cancer screening and uterine cancer screening are recommended, beginning at a young age. Other screening may be recommended based on family history.
Multiple endocrine neoplasia type 2A (MEN2A) results from an abnormal alteration in the RET gene. Family members have an increased chance of developing medullary thyroid cancer, hyperparathyroidism (overactive parathyroid gland) and tumors of the adrenal gland (known as pheochromocytoma). Removal of the thyroid gland is recommended.
Von Hippel Lindau (VHL) syndrome results from an abnormal change in the VHL gene. Families with VHL syndrome have an increased risk of developing kidney cancer, tumors of adrenal gland (pheochromocytoma), as well as eye, brain and spinal tumors. Tumors found on the retina, located in the back of the eye, are characteristic of this syndrome. Evaluations of the eyes, kidneys, brain and spinal cord are recommended on a yearly basis.
Siteman Cancer Center’s hereditary cancer program has experience with these and other types of hereditary cancer syndromes.
Cancer risk assessment and education
At the Siteman Cancer Center, genetics evaluation begins with risk assessment and education. A genetics physician and genetic counselors work with individuals to determine whether the cancers in their family truly suggest a hereditary tendency. The first step involves taking a detailed family history to determine which family members had cancer along with their age at onset and whether they developed other cancers as well.
This information is important because hereditary cancers tend to occur at an earlier age, and people with an altered cancer gene have a greater risk of developing more than one cancer. With a complete family history and personal medical history, patients can be given a rough estimate of their lifetime risk of developing certain types of cancer. They then can consider screening and risk-reducing options based on the level of their risk.
Various considerations help in making this assessment. The risk increases, for example, when many family members or multiple generations are affected or when family members have developed cancer at an unusually early age or in both sides of an organ, such as both breasts.
Typically, a genetic counselor helps patients document their family history and collect available medical records of family members with cancer when necessary.
The next step is for patients to meet with a genetics physician and genetics counselor to assess their family-based cancer risk and discuss appropriate surveillance procedures. If a cancer risk appears to be hereditary, genetic testing may be useful in identifying the most appropriate medical care.
Genetic testing to identify a specific gene alteration may be recommended for high-risk families. It is typically performed using a blood sample. Not all people who pursue cancer risk assessment decide to have genetic testing.
Like all tests, genetic testing has benefits and limitations and entails many practical, medical and emotional implications. The most information can be gained when a family member with cancer is tested first so the gene alteration can be identified. However, this may not always be possible.
Even if an individual at high risk is found to carry an altered gene, genetic testing cannot determine if cancer is present or when it may develop. It can only confirm an inherited predisposition or increased risk for certain types of cancer.
Despite its limitations, genetic testing can be valuable. Results can help individuals make some medical decisions, such as determining the best plan for cancer screening or whether to pursue preventive medical or surgical therapies.
Clinical genetics assessment
Approximately 5 percent to 10 percent of all cancers occur as a result of hereditary or genetic factors that are passed on in families. This statistic should be reassuring: Although many people have relatives who had colon or breast cancer – types of cancer that are common in the population – the majority should not be concerned they are particularly susceptible to these cancers simply because a family member had them.
Hereditary cancer typically results from an abnormal alteration in a single gene that may then be passed on in a family. People with this altered gene have a significantly higher chance of developing certain times of cancer.