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School of Medicine
Who should be referred to a clinic like Johns Hopkins for genetic counseling?
Anybody who has:
- Multiple family members who are diagnosed with colorectal cancer
- A family member under the age of 50 who was diagnosed with colorectal cancer
Someone who is concerned about his or her risk for colorectal cancer because there is a history of colorectal cancer in that person’s family may also benefit from genetic counseling as a means to reduce anxiety.
How has our understanding of familial colorectal cancer changed in the last few years?
It has long been known that when multiple family members were diagnosed with colorectal cancer, there was a higher risk for other family members to develop cancer. However, it wasn’t known why that was so.
Within the past few years, researchers have identified certain genes that are associated with colorectal cancer syndromes. That knowledge makes it possible to look at the genetic makeup of a family member diagnosed with colorectal cancer to determine if there is a change in one of those genes that can be associated with colorectal cancer. If that change is found, then other family members can be tested.
Those who don’t have the genetic change can follow the same cancer screening guidelines as the general population. For family members who have that genetic change, doctors will recommend more intensive surveillance and screening.
Is there a blood test available to determine if you did inherit a specific gene mutation?
Genetic testing is usually done through a blood test, but the tests are not routinely offered to everybody with a family history of colorectal cancer. Genetic testing is offered to families whose history makes clear that colorectal cancer is probably associated with a certain gene. People who are concerned about their family history can meet with a genetic counselor to determine if that testing is appropriate or if it would not be helpful.
What should a person look for in his or her family history to determine if there is a possibility of a genetic connection to cancer?
People should look for:
- Multiple family members diagnosed with colorectal cancer. If someone has three or more family members who have been diagnosed with colorectal cancer, it’s a good idea to look into genetic testing. If a grandparent or aunt and uncle has been diagnosed with colorectal cancer, along with one or more first-degree relatives (parent or sibling), there is a higher chance that there is a genetic component to the cancer since it may be passed down.
- Age of family members diagnosed. People who have family members who were diagnosed with colorectal cancer under age 50 should ask a doctor about genetic testing.
- The presence of multiple colorectal polyps. There is a genetic condition associated with multiple polyps, and testing is available for that.
- Family history of other cancers. Colorectal cancer can be seen with uterine cancer and ovarian cancer. If those cancers are also diagnosed in a family, genetic counseling may be useful.
- Ashkenazi Jewish ethnicity. A specific gene mutation has been identified in the Ashkenazi Jewish population, so testing for people of Jewish descent with a family history of colorectal cancer is a good idea.
If someone has the blood test and it is positive for the genetic mutation, will that person definitely get colorectal cancer? And if not, what percentage will?
Not everyone who is positive for the genetic mutation will develop colorectal cancer. The possibility varies depending on the genetic mutations that are present. Mutations in at least six different genes can be associated with colorectal cancer risk:
- Familial adenomatous polyposis (FAP) (which results in the development of numerous colorectal polyps) carries a 100 percent lifetime risk of developing colorectal cancer.
- Mutations associated with hereditary nonpolyposis colorectal cancer (HNPCC) carry a lifetime risk of about 80 percent.
- The genetic mutation associated with being of Ashkenazi Jewish descent is about 20 to 30 percent.
Please describe familial adenomatous polyposis
Familial adenomatous polyposis (FAP) is a condition in which people develop hundreds to thousands of polyps in their colon and GI tract. It does carry about a 100 percent lifetime risk for developing colorectal cancer. It is associated with mutations in the APC gene.
In addition to the presence of polyps in the colon, people with FAP may also have:
- Bony tumors on the jaw, the skull or limbs
- Cysts on the skin
- Teeth not erupting in the normal way
- Changes in the retina of the eye
- Fibrous tumors in the abdomen
Please describe hereditary nonpolyposis colorectal cancer
Hereditary nonpolyposis colorectal cancer (HNPCC) is associated with other cancers, including those in the uterine, ovarian, stomach, small intestine, urinary tract and bile ducts. When those cancers are present in a person’s family history, there is a possibility of HNPCC.
Another sign of HNPCC is early onset of colon cancer. The average age of diagnosis is in the early forties, about age 44, but people as young as their twenties may be diagnosed with colorectal cancer if they have HNPCC.
Most colorectal cancer that is associated with HNPCC is a right-sided colorectal cancer, occurring in the cecum area or the ascending colon section, though researchers don’t yet know why that is.
Five genes are now known to be associated with HNPCC. An individual who has a mutation in any of those five genes has about an 80 percent lifetime risk of developing colorectal cancer.
If a person looks at his or her family tree and does not see a cluster of colorectal cancer but does discover uterine or ovarian cancers, should that be a cause for concern?
Yes. It means the person should speak with his or her doctor to determine if genetic counseling is a good idea.
What percentage of all colorectal cancers are inherited?
Five to 10 percent of all colorectal cancer is considered hereditary.
How do the screening recommendations differ for high-risk groups versus the general population?
For the general population, colorectal cancer screening, most commonly done through a colonoscopy, does not need to start until age 50. For those at higher risk, screening recommendations will vary depending on the genetic mutation:
Familial adenomatous polyposis (FAP): The recommended screening procedure is a flexible sigmoidoscopy to find polyps in the lower colon. If polyps are found in the lower section of the colon, then they are likely to be throughout the colon. Screening usually begins with children between the ages of 10 and 12, because the polyps will begin to develop at around age 15, and the first screening should occur before the polyps develop.
It is generally recommended that the colon be removed once the polyps develop because the risk is very close to 100 percent that colon cancer will develop.
Hereditary nonpolyposis colorectal cancer (HNPCC): The recommended screening procedure is a colonoscopy, which should be done either annually or every other year beginning between the ages of 20 and 25. HNPCC carries about an 80 percent risk of colorectal cancer so detecting and removing precancerous lesions, like polyps, is critical to preventing cancer.
Are colonoscopies recommended for the general population after age 50?
It is recommended that people age 50 and older be screened for colorectal cancer and that screening can be done in a number of different ways, including a colonoscopy, which is the most common method used. Screening procedures include:
- Checking the stool for blood annually
- Flexible sigmoidoscopy every five years
- Barium enema X-ray every five years
- Virtual colonoscopy every five years
- Stool DNA testing and colonoscopy every 10 years
Can people who are at higher risk offset that risk by modifying their diet and lifestyle?
Everyone should eat a diet that is high in fiber and low in fat. They should make sure to get at least five servings of fruit and vegetables daily and eat red meat rarely. They should not smoke and should try to get daily exercise. Doing these things may potentially decrease the risk of colorectal cancer.
However, it is not presently known if changing and improving lifestyle factors can offset the risk associated with gene mutations that lead to a higher risk of colorectal cancer. While it’s not likely to completely offset the risk, it may modify the risk. If someone has a genetic mutation that would lead to the development of colorectal cancer at 40, that person may be able to delay the development of cancer until the age of 60 by making dietary and lifestyle changes.
Keep in mind that there is not a lot of data that indicates how lifestyle and dietary changes affect the development of colorectal cancer in people with genetic mutations. But a healthy diet and lifestyle will not hurt.
Is Johns Hopkins involved in any clinical research studies that people who have a higher genetic risk of developing colorectal cancer can participate in?
Yes. There is a hereditary colorectal cancer registry at Johns Hopkins, which is a list of thousands of families who are suspected of having hereditary forms of colorectal cancer. Every time a research study examining some aspect of colorectal cancer comes up, participants are drawn from that registry. They can then decide to participate or not. If someone is interested in taking part in a research study, then he or she should sign up through the registry.
There are also studies that offer genetic testing for people in high-risk families, in which researchers are looking for genetic factors in addition to those that are now known.