The DNA you were born with contributes to your risk of developing cancer. But is cancer hereditary?
If you are reading this, you may have a family member with cancer and are concerned about your own risk of developing the disease. Understanding whether cancer is caused by an inherited mutation can help clarify the risks of developing cancer and help determine appropriate medical options for disease screening and prevention.[sc: inlinead]
Is Cancer Hereditary? Understanding Cancer Risk
Heredity describes the passing of DNA (genetic information) from parent to child. Although many people have a family member with a history of cancer, the vast majority of cancers are not due to heredity.
Most cancers occur by random chance, often the result of environmental conditions or lifestyle choices, or just normal aging. As people get older their DNA randomly develops changes over time; sometimes these random changes can result in cancer during old age.
Most cancers occur by random chance, not by inherited DNA.
In some families, however, cancer may occur at higher rate than expected by chance alone. However, most families with a history of cancer do not have an identifiable genetic cause.
Scientists are working to determine which of these families has cancer related to specific inherited DNA according to the following groupings:
- Sporadic – Cancer that occurs by random chance. Individuals with sporadic cancer do not have a family history with the same type of cancer.
- Familial – Cancer that occurs by a combination of genetic and environmental risk factors. Individuals with familial cancer may have family members with the same type of cancer; however, there is no clear pattern of inheritance (e.g., the disease risk is not clearly inherited from parent to child).
- Hereditary – Cancer that occurs when specific DNA is inherited from parent to child. Individuals with hereditary cancers are more likely to have family members with the same, or similar, type of cancer. Hereditary cancers often occur at an earlier than average age.
People who inherit DNA associated with cancer risk will not necessarily get cancer; however, their risk of developing cancer during their lifetime is higher than average.
Inherited genes do not necessarily mean a person will get cancer.
What Percentage of Cancers are Caused by Hereditary?
The percentage of cancers caused heredity varies by the specific type of cancer. In general, only about 10% of cancer is hereditary.
Pie Chart: Is Cancer Hereditary? Percentage By Cancer Type
For example, most breast cancer is not hereditary. In the U.S., only 5-10 percent of breast cancers are related to an inherited genetic change. About 10-25% of ovarian cancer is linked to inherited genetics, whereas around 10% of colorectal cancer is associated with inherited genetic risk.
Bar Graph: Percent of Tumors with Inherited Mutations by Cancer Type
Is Hereditary Cancer Detectable By Genetic Testing?
Sporadic and familial cancers are not detectable by DNA testing; this means over 90% of cancers would not be detectable by genetic testing. Furthermore, only certain risk genes for hereditary cancers are detectable.
Why aren’t all hereditary cancers detectable by testing? This is because current DNA tests detect only a very limited number of potential genetic changes associated with cancer risk. Additionally, thousands of potential genes and thousands of potential genetic changes are associated with hereditary cancer risk. Only a small handful of these cancer-risk mutations are identified.
For example, current DNA testing can only detect a handful of genetic mutations which contribute to hereditary breast cancer. Of the known risk genes associated with breast cancer risk, only 45 percent can explain inherited breast cancer risk, while the other 55 percent are still unexplained. [Source: Couch, Mayo Clinic, 2015]
Even for the known risk genes, wide-scale testing may not ever be feasible, due to the vast number of potential genetic changes which may increase hereditary risk.
DNA testing identifies a few cancer risks — not all.
Based on your family history and/or genetic test results, please consult with a medical professional and genetic counselor to discuss ways to reduce your lifetime cancer risk.[sc: bottomad]
The Genetics of Cancer, National Cancer Institute
Familial Cancer Program, Mayo Clinic