Cancer Risk: Know Your Genetic Blueprint

Understanding Hereditary Cancer, Genetic Testing, and the Risks

Genetic testing in medical lab
Victor Torres/Stocksy United

What exactly is hereditary cancer? With talk about genetic screening tests and "breast cancer genes," many people have started wondering if cancer is "written in the stars." So, it's important to understand what a genetic predisposition really means, as well as what you can do to lower your risk if you have a family history of cancer.

What Is Hereditary Cancer or Genetic Predisposition?

Hereditary cancer refers to cancers that are more likely to occur in some people than others based on their genetic blueprint.

Hereditary cancer is a cancer that has developed as a result of a gene mutation or other genetic abnormality passed down from a parent to a child. Inheriting a gene mutation does not necessarily mean you will develop cancer, but it certainly increases the risk (compared to someone who has not inherited a mutated gene). Cancers that occur in people with these genetic abnormalities are referred to as "hereditary cancers."

Cancer is not inherited, instead, you inherit a gene (or combination of genes or other genetic abnormality such as translocations and rearrangements) that can predispose you to cancer, and that predisposition can be very small or very large, depending on the particular gene and other risk factors or combination of genes. 

Having an inherited gene mutation that can lead to cancer means that you have a "genetic predisposition" for cancer — that is, you have a higher risk for developing cancer than the general population.

Genetic Mutations and Cancer

There are two types of genetic mutations that can lead to cancer:

  • Hereditary mutations
  • Acquired mutations

Genetic mutations underlie the development of cancer, but not all cancers are hereditary, as most cancers are the results of acquired gene mutations (mutations that occur after birth).

Over our lifetimes, our genes accumulate mutations as a result of exposure to carcinogens (substances that cause cancer), but also due to the normal metabolic processes of cells:

  • Each time a cell divides, it must make an exact copy of all the DNA in a cell. 
  • This DNA can become damaged (mutated) simply as an accident during the process of dividing. 
  • Mutations caused during the dividing process is the reason that cancer becomes more common the older we get. It is also the reason that chronic inflammation, such as the kind that occurs in the mouth and lungs with smoking, may result in cancer.
  • Most of the time that this damage to DNA occurs, it is either repaired, or the cell goes through a process of programmed cell death (apoptosis).

The reason we don't all get cancer all the time is that we have methods for repairing the inevitable damage that occurs in our DNA. Some of our genes are called tumor suppressor genes. Tumor suppressor genes code for proteins that repair damaged DNA in our cells.

When tumor suppressor genes are mutated, they code for proteins that don't work as well at doing this repair work, and damaged cells are allowed to live and multiply and eventually become a tumor (cancer).

What Causes Cancers to be Hereditary?

Each parent passes a copy of their genes to their child so that the child is born with two copies of each gene in their body (one from the mother and one from the father). Most people are born with two normal copies of each gene, but for someone with an inherited mutation in one copy of a tumor suppressor gene (that normally protects against cancer) means that the risk for cancer is increased. 

Two common tumor suppressor genes are the BRCA1 and BRCA2 genes. Hundreds of different types of mutations in either of the BRCA1 and BRCA2 genes have been identified, some of which have been determined to be harmful and increase the risk of cancer if the mutated genes are passed on to offspring.

Family History of Cancer: Are You at Risk?

It is important to note that there are some cancers that are much more likely than others to have a genetic component. There are also cancers that run together in clusters. For example, if someone has a family history of early-onset breast cancer and other relatives with pancreatic cancer you might suspect a BRCA2 gene mutation. People with colon cancer have a slightly increased risk of developing breast cancer. In determining risk, genetic counselors look at several factors:

  • The number of relatives who have had cancer (both specific cancers and any cancer.)
  • The types of cancer (as noted previously, some cancers are more likely to run in the family than others.)
  • The combination of cancer types - It's often not realized that a combination of cancers may be considered to have a greater genetic link even than two family members having a cancer at one site. For example, a BRCA2 gene mutation may have been a predisposition for breast cancer in one relative, ovarian cancer in another, prostate cancer in a 3rd, and pancreatic cancer in a 4th. A combination such as this may be of more concern than finding breast cancer in six or eight relatives. What this means is that everyone should take a very careful family history of cancer in their families to discuss with their physicians.
  • Cancer and gender - An example of gender having an effect on familial cancer risk is breast cancer, where breast cancer in men is more likely to have a genetic component than breast cancer in women.
  • The number of relatives with a disease is also important. Certainly, your risk of developing colon cancer is greater if your mother, uncle, and brother had the disease instead of having only one of these relatives with the disease.

Compiling your complete family history can help you gauge if you are genetically predisposed to cancer. Some people may choose to pursue genetic testing to know if they carry a mutated gene. At a minimum, and now that we have several genetic tests available, everyone should write out a thorough history of cancer in their extended family to review with their primary care doctor at the time of a physical.

Genetic Counseling and Testing

It is important to go through genetic counseling if you are considering genetic testing. One reason is so that you understand the testing procedure and results and are prepared for whatever the answer may be.  More importantly is that trends in risk may be noted for which there are not yet tests available, but based on history alone it may be recommended that you have additional screening tests performed.

Genetic testing may sound as simple as a quick blood test, but it's not that simple. As a quick example, if you have a family member who had breast cancer and a particular mutation in the BRCA2 gene, that particular mutation could be tested for. Otherwise, a full panel just to evaluate all mutations in the BRCA2 gene alone may cost several thousand dollars. Considering this is just one genetic test, you can see where this is going.

In time and with the completed human genome project, this type of testing should improve, but the science is still, in many ways, in its infancy.

Some points to consider and discuss with a genetic counselor before you have genetic testing done include:

  • What would you do and how would you feel if you learned you had a genetic predisposition to some type of cancer?
  • How accurate are the results?
  • What does the test really tell you?
  • What are the limitations of the test?

Genetic testing may tell you that you are predisposed to one particular gene mutation which can predispose you to one particular form (or more) of cancer. For most cancers, there is a fear that genetic testing will give people false assurance about lack of risk. Let's take a look at a few cancers.

Breast Cancer: Is It Genetic?

Breast cancer certainly runs in families as roughly 10 percent of breast cancers are considered "genetic."

Many people are familiar with the BRCA1/BRCA2 gene mutations and breast cancer. When Angelina Jolie had her preventive mastectomy due to one of these mutations, the public became interested in testing for these genes. Unfortunately testing for these genes is not as simple as just taking a "blood test" as there are many ways in which the BRCA1 and  BRCA2 genes can be mutated.

BRCA1 and BRCA2 are tumor suppressor genes. These genes are inherited in an autosomal recessive pattern, meaning that both copies of your gene need to be mutated in order to develop breast cancer. If you are considering testing, don't miss these thoughts on whether or not you should you have the breast cancer gene test.

The genetics of cancer is actually much more complicated than this. For example, there can be mutations in oncogenes — genes that are like the accelerator driving a car. With these mutations there may only need to be a mutation in one copy of the gene (autosomal dominant.) In contrast, many tumor suppressor genes are inherited as noted above. In addition, there are many other factors and mechanisms too complicated to address here, and most cancers are caused by a combination of several mutations (with a few important exceptions) including both oncogenes and tumor suppressor genes, with most mutations, again, occurring after birth.

Prostate Cancer

Prostate cancer can also run in families, and there appears to be a link between prostate and breast cancer.

If you have a family history of prostate cancer, make sure to talk to your doctor. For example, PSA testing can save lives, but it is not for the ill-informed. Prostate cancer has a high genetic link, since the inherited risk of prostate cancer is estimated to be as high as 60 percent, although only 5 to 10 percent is thought to be related to genetic susceptibility genes. If your father or brother have had prostate cancer, your risk is more than double that of someone without a family history of the disease.

Predisposition to Colon Cancer

There are several things to understand with colon cancer — or several "types" of predisposition. Overall around 20 percent of people who develop colon cancer have a family history of the disease. A predisposition to colon cancer can be passed on in a few ways:

Other Cancer and Genetics

Some hereditary predispositions to cancer span many cancers, and several cancers in addition to the ones mentioned above have a genetic component. Many people aren't aware of some genetic risks, for example, that 55 percent of a person's melanoma risk is due to genetic factors, or that, women who smoke who have the BRCA2 mutation have twice the risk of developing lung cancer. This simply stresses why it is so important to talk to your doctor and share a careful family history.

Could a Gene Test Make You Lose Your Insurance?

The Federal Health Insurance Portability and Accountability Act (HIPAA) prevents discrimination against people based on gene tests for cancer with regard to ability to get health insurance. That said, it is important to consider possible ramifications of gene testing relative to future applications for life insurance and other possible conditions in which you may be asked about such tests.

Is a Genetic Predisposition to Cancer Always Bad?

Perhaps that was a sly way to bring up an important and final point. Certainly, you never want to be predisposed to cancer, or carry a gene that is associated with developing cancer. But having an awareness of genetic risk — and acting upon that awareness — may leave you in an even better place than if you did not have the risk. How so?

Roughly 10 percent of breast cancer is considered genetic, meaning 90 percent is not. Many women with a family history of breast cancer are very careful about screening and quickly see their doctors if they have a lump. For those without a family history, there may be a lack of the same awareness or she may think that maybe the lump isn't anything because there isn't a family history. In this theoretical scenario the woman with the hereditary link may take action more quickly — and have her breast cancer diagnosed at an earlier more curable stage of the disease — than the woman without the family history.

Non-Genetic Cancer May Run in Families

As a final note, make sure to follow a cancer prevention lifestyle. Some cancers that appear to run in families may not be genetic at all and instead due to a common exposure. An example would be a family of non-smokers who all develop lung cancer. Instead of this being a genetic link, it may be that all of them were exposed to radon in the home.


American Society of Clinical Oncology. Cancer.Net. The Genetics of Cancer. Updated 08/2015.

Hall, M., Obeid, E., Schwartz S., Mantia-SMaldone, G., Forman, A., and M. Daly. Genetic testing for hereditary cancer predisposition: BRCA1/2, Lynch syndrome, and beyond. Gynecologic Oncology. 2016. 140(3):565-74.

National Cancer Institute. Cancer Genetics Overview – Health Professional Version (PDQ). Updated 01/15/16.

National Cancer Institute. The Genetics of Cancer. Updated 04/22/15.

National Cancer Institute. Genetics of Prostate Cancer – Health Professional Version (PDQ). Updated 02/12/16.

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