National Institutes of Health
Inherited Risk
We all face risks every day of our lives: we steer clear of the hazards of our environment, wear seatbelts, and take routine steps to preserve our health.
We all know that risk is a part of living, but not everyone understands that risk can also be something we carry as part of our genetic makeup.
A higher risk for cancer can run in families. Below you'll find information on inherited risk, including sections on:
- Heredity 101
- Genes Can Change
- Mutations Sometimes Lead to Cancer
- Family History
- Which Relatives Are Important When Thinking About Hereditary Risk?
- How a Hereditary Condition Can Be Passed on
- How Risk Can Vary by Population
- Hereditary Breast and Ovarian Cancer (HBOC) 101
- What Causes HBOC?
- Other Mutations
Inherited risk for breast and ovarian cancer no longer means that cancer is inevitable. In other sections of this site, you'll learn why.
Back to TopHeredity 101
We all know the phrase "it runs in the family." From an obvious family resemblance to a not-so-obvious inherited trait such as the shape of our earlobes, much of who we are physically comes from our DNA—and our DNA comes from the DNA of our two biological parents.
The Human Genome Project estimates that we have between 20,000 and 25,000 genes. The genes in our DNA are like a tool kit, used by different cells in different ways. Most cells use only a few of the many, many possible functions our genes have.
Genes Can Change
All cancers are caused by gene mutations—changes in a person's DNA. Most of these changes do not cause cancer.
In fact, these changes happen regularly—usually by chance. For example, when cells divide to produce new cells, a mistake can happen that introduces a tiny change. Fortunately, these random mistakes are usually repaired by your body.
Sometimes, however, when these changes are not repaired, the mistake gets copied and repeated as the cells with the mistake divide again and again. When mistakes accumulate or interfere with a critical function such as gene repair, a mutation can lead to cancer.
Mutations Sometimes Lead to Cancer
Shown above, a series of random mutations creates cancer cells. Mutations can also be inherited—part of your genetic makeup from birth.
For cancer, two kinds of gene mutations are important:
- Random—the mistakes that occur in DNA by chance and get repeated. These mistakes are more likely to happen as you get older. Being exposed to radiation or certain chemicals can also make genetic changes more likely
- Inherited—the genetic changes that a person is born with, passed on by the person's father or mother or both
Most cancers develop from random mutations, but up to 10 percent come from genetic changes passed on by a parent. Certain inherited genetic mutations can make it much more likely that a person carrying the mutation will get cancer—and get cancer earlier.
But, please note, sometimes a family will appear to have a hereditary cancer when what they really share is a common living or working environment that exposes them to radiation or chemicals that can cause mutations. Your doctor can help you learn more.
If you do carry an inherited mutation that has been linked to cancer, knowing your risk can help you and your doctor make better, more informed decisions about your health, possibly before cancer has a chance to develop.
“All cancer is genetic, in that it is triggered by altered genes. Genes that control the orderly replication of cells become damaged, allowing the cells to reproduce without restraint”
— National Cancer Institute, National Institutes of Health
Family History
When talking about your genetic heritage, the only family history that matters is the history of relatives with whom you have a direct biological connection. For example, if your father has a brother, he is your uncle—a biological second-degree relative. If he marries a woman, she becomes your aunt, but is not a biological relative. If she has a child, however, that child is your first cousin—a biological third-degree relative.
Which Relatives Are Important When Thinking About Hereditary Risk?
| First-degree Relatives |
Second-degree Relatives |
Third-degree Relatives |
| Biological mother, biological father, full biological sibling, or biological child (stepparents, stepchildren, or half siblings are not first-degree relatives.) | Biological grandparents, biological aunts and uncles, biological nieces and nephews, half siblings, or biological grandchildren | Biological first cousins, great-grandparents, great-aunts and great-uncles |
People with a family health history of a particular disease can take action to reduce their risk of developing the disease. To learn more about your biological inheritance, you'll want to talk to your relatives, gather information, and fill out a pedigree—a family tree. If you find that certain illnesses, such as breast or ovarian cancer, have appeared in more than one relative, you'll be ready to talk with your doctor and investigate further.
Use the U. S. Surgeon General's free My Family Health Portrait tool to create a personalized family health history report. The site uses a secure connection to keep your personal and family information private.
If you decide to put together a family tree, be sure to look deeply on your father's side. If there is HBOC on your father's side of the family, it can involve more distant relatives than on your mother's side.
How a Hereditary Condition Can Be Passed on
How Risk Can Vary by Population
Just as an increased risk of cancer can run in families, some inherited conditions are more likely to occur among particular population groups. People in these groups may have inherited a certain genetic makeup from the ancestors they share. If the genes that are common to a group include a genetic mutation that can cause a specific disease, that disease can occur more frequently in the group. Hereditary breast and ovarian cancer (HBOC) syndrome, for example, is more common in people of Ashkenazi, or Eastern European Jewish, ancestry.
“When a gene with a mistake is passed along in family members, it is called an inherited altered gene. All people have altered forms of some genes. Certain altered genes can increase your risk of illnesses such as cancer.”
— The National Cancer Institute, National Institutes of Health
Hereditary Breast and Ovarian Cancer (HBOC) 101
Hereditary breast and ovarian cancer (HBOC) syndrome is not a cancer. If you have HBOC, you carry a gene mutation you inherited from your father, your mother, or sometimes both parents, that significantly increases your risk for certain cancers.
In fact, people with HBOC have up to 50% risk of breast cancer by age 50 and up to 44% risk of ovarian cancer by age 70. If you do have an increased risk, you can take measures to prevent cancer from occurring, or be sure to detect it early.
Many people are unaware of their inherited risk, though they may be aware of a cancer history in their family. You should consider talking with a doctor about hereditary breast and ovarian cancer (HBOC) syndrome if at least one of the following applies to you:
- Breast cancer before age 50
- Two or more relatives who've had breast cancer
- A male relative who's had breast cancer
- Breast cancer in both breasts or twice in the same breast
- Breast cancer and are of Ashkenazi, or Eastern European Jewish, ancestry
- Ovarian cancer at any age
What Causes HBOC?
After studying several families in which many people developed breast or ovarian cancer, researchers found alterations in two genes. The first, BRCA1 (for BReast CAncer gene), was discovered in 1994, and the second, BRCA2, in 1995.
The BRCA1 and BRCA2 genes normally help to regulate cell growth. That's an important role—as important as having brakes on your car. When mutations interfere with the assigned role of these genes, the body's defenses against cancer can be weakened.
An inherited alteration in either the BRCA1 or the BRCA2 gene causes about 10% of breast and ovarian cancer. These mutations—and possibly others yet to be identified—can also increase the risk of several other types of cancer, including pancreatic, prostate, and colon cancers.
BRCA1 and BRCA2 mutations can come from either the father or the mother. Someone who carries a BRCA1 or BRCA2 mutation with a known link to breast and ovarian cancer is said to have hereditary breast and ovarian cancer (HBOC) syndrome. A person with HBOC not only has a higher risk of developing these cancers, but also may pass that gene mutation on to his or her children.
Other Mutations
Not all multiple cases of breast or ovarian cancer in families are linked with BRCA1 or BRCA2 mutations. Research may eventually identify other genes associated with HBOC.
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