Understanding the Genetics and Genomics of Cancer

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.


The role our genes play in cancer continues to be a strong area of research. Learning how genes and mutations cause cancer is important to developing new screening methods and new therapies.

All cancers are caused by genetic mutations, which are changes that occur in DNA. These can be inherited from your parents’ germ cells (egg and sperm cells that form an embryo), or they can be acquired, which develop over time. Inherited mutations are also known as germline mutations, and acquired mutations are also known as somatic mutations.

Today, doctors can test for these mutations with genetic and genomic testing. Although the words are often used interchangeably, they do not mean the same thing.

Genetics vs. Genomics

Genetic testing is used to determine if you have inherited a mutation that increases your risk for developing cancer. If you have a family history of a particular type of cancer, you may consider genetic testing to see if you carry the gene. Identifying hereditary cancers through genetic testing allows people at an increased risk to be monitored more closely for the development of cancer. Having an inherited mutation doesn’t mean you will automatically develop cancer; it only means the risk is increased and you can explore ways to lower the risk, such as surgery, medication, frequent screenings or lifestyle changes.

Doctors now look for certain risk factors that may indicate a hereditary cancer is possible. They consider the following:

  • Family history of cancer
  • Cancer at an early age
  • Multiple cancers in one relative
  • Rare cancers
  • Ancestry, such as Ashkenazi Jewish heritage

Genomic testing examines a cancer’s genes, which may reveal mutations that could indicate the cancer’s behavior, how aggressive it might be and if it will metastasize (spread). This information helps doctors choose treatment options. In certain cancers, mutations have been discovered that can be treated with targeted therapy, which is designed for a specific mutation. Genomic testing is also used to detect biomarkers, which are substances such as genes or molecules that can be measured in the blood, plasma, urine, cerebrospinal fluid or other body fluids or tissues. They are produced by cancer cells or other cells of the body in response to cancer. Also known as tumor markers, biological markers or molecular biomarkers, they are routinely tested for in certain cancers.

Biomarkers may be prognostic, predictive or diagnostic. A prognostic biomarker provides information about a person’s overall cancer outcome, regardless of therapy, while a predictive biomarker gives information about the effect of a specific treatment approach. Diagnostic biomarkers help determine the type of tumor. Some biomarkers may also help determine how aggressive (fast growing) a tumor is and may predict long-term survival.

The Role of a Genetics Counselor

Seeking genetic counseling from a genetic counselor before getting tested will help you prepare emotionally for the results. This counselor has special training to help you understand the risks and benefits of genetic testing and can explain the limits of testing. After genetic testing, your counselor will help you understand your test results and their potential effect on you and other family members and will provide counseling and support. Family members may be offered testing if a mutation is found.

Before meeting with a genetic counselor, gather the following information, if it’s available.

  • Your medical records, doctor notes and pathology reports
  • List of family members, including current ages or age at death and cause of death
  • Specific cancers diagnosed within the family

Genetic and genomic test results become part of your medical records, which are protected by the Health Information Portability and Accountability Act (HIPAA) and may only be shared with people who have legal access to these records.

The Importance of Sharing Your Family Health History

Choosing to get genetic testing is a decision that affects your entire family. Knowing and sharing the information could help them be screened and monitored closely if they have a gene mutation associated with cancer. Preventing or detecting a cancer early offers the best chance of a successful treatment outcome.

Keep in mind that not all family members may want to share their health information or receive the results of your testing. Learning these results can bring up a range of emotions including feelings of acceptance, relief, hope, confusion, denial, anger and guilt.

The results may be complicated and difficult to interpret. A genetic counselor can be crucial to help you understand what the results mean for you and your family and their future health.

Once you understand your results, you can choose to share them with your children, siblings, nieces, nephews, etc. Be prepared that your relatives may not want to know or do anything about the information. Each must make the decision about what to do with the information.

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. 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

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


Register Now! Sign Up For Our Free E-Newletter!

Read Inspiring Cancer Survivor Stories

Order Your Guides Here