Mom Genes: How Your Family History Affects Colon Cancer Risk
Fast Facts
- People with a first degree relative (parent, son, daughter or sibling) diagnosed with colon cancer before age 60 have an increased risk of getting colon cancer. The risk can be twice that of someone without relatives diagnosed with colon cancer.
- Mutations in certain genes that either cause colon cancer, or protect against it, can be passed from parents to their children.
- If a family member is diagnosed with colon cancer, the doctor may suggest looking for a gene mutation in that person’s DNA. If a mutation is found, the doctor will likely recommend that close family should be tested, too.
More than 1 in 20 people will be diagnosed with colon cancer in their lifetime. About 30% of colon cancer is “familial,” meaning that it’s more likely to run in certain families. But less than 10% of colon cancer is “hereditary,” meaning that it is passed from a parent to a child through a gene mutation. It’s important to know the differences between familial and hereditary because it affects risk, types and frequency of testing, and chances of passing colon cancer genes on to your children. Let’s take a look at how they differ.
Familial vs. genetic colon cancer risk:
Doctors have identified at least 4 gene mutations that are directly linked to developing colon cancer. These “genetic colon cancers” account for about 5-10% of all colon cancers diagnosed every year. If a person has one of these abnormal genes, they are several times more likely to be diagnosed with colon cancer than someone who doesn’t have that gene. If the gene mutation is in a person’s sperm or eggs, they can pass the gene on to their children. This increases the risk that the child will develop a colon cancer syndrome at some point in their lifetime.
On the other hand, colon cancer also “runs in the family” in some cases. Doctors may not be able to find a specific gene mutation in most of these cases. That doesn’t mean the cancer isn’t genetic, it just means that doctors don’t have a test for that gene yet. Colon cancer that runs in the family accounts for about 30% of all cases of colon cancer.
What are the types of genetic colon cancer?
There are many different genetic syndromes associated with an increased risk of colon cancer. Genetic colon cancer mutations can cause cancer in a number of ways:
- Mutations in tumor suppressor genes (genes which stop cancer from forming)
- Mutations in proto-oncogenes (genes that promote cancer)
- Microsatellite mutations (causes the two strands of DNA to mismatch and not repair)
Oncologists (cancer doctors) divide genetic colon cancers into 2 types:
Hereditary non-polyposis colorectal cancer (HNPCC)
- Only a single gene from one parent is needed to cause cancer (autosomal dominant).
- Lynch Syndrome is the most common type of this genetic cancer.
- People with this type of colon cancer are at increased risk for other cancers including endometrial, small bowel, stomach and ovarian cancer.
Hereditary polyposis colorectal cancer (HPCC)
- Most forms of polyposis colorectal cancers are autosomal dominant.
- Familial adenomatous polyposis syndrome is the most common type of this genetic cancer. Other, rarer, syndromes include juvenile polyposis coli, PTEN hamartoma syndrome, Peutz-Jeghers syndrome, Gardner syndrome, Cowden syndrome and others.
If I have a bad gene, does it mean I’ll get colon cancer?
The short answer is no. Having the gene for any type of colon cancer puts you at increased risk, but it’s not a guarantee you’ll be diagnosed. For example, people with Lynch syndrome have about a 75% chance of developing colorectal cancer at some point. Compare that to about 5% in the average population. Each genetic syndrome has a different risk of developing into colon cancer. Doctors can assess risk based on the syndrome and other factors. This can help you determine how often to get screened for colon cancer and other associated cancers.
What if colon cancer runs in my family?
Even when people have a strong family history of colon cancer, doctors usually can’t find a genetic mutation. There are probably genes at work that we don’t have a good test for. Other risk factors that family member have in common that can influence the risk of colon cancer include:
- What you eat: If your family eats a lot of highly processed foods, you’re more likely to eat the same foods which puts you at risk
- Smoking: Smoking is often a family habit
- Weight: Obesity runs in families
- Exercise: Parents who are active tend to have children who are active
- Environmental exposure: Everyone in a household breathes the same air and drinks the same water for much of the day and night
Keep in mind that these same risk factors also increase the risk for colon cancer in people with inherited cancer risk.
How does family history affect colon cancer screening?
Colon cancer screening should begin at age 45 for all Americans. If you have an increased risk of colon cancer due to family history or genetics, the recommendations are different. Depending on your set of circumstances, your doctor may suggest:
- Screening before age 45
- Screening more frequently than recommended for low-risk individuals
- Using specific screening tests that allow directly looking at the colon (colonoscopy)
- Genetic testing on you or your family members
- Beginning earlier and more frequent screening on close family members
- Screening for other types of cancer
The bottom line
Colon cancer is one of the biggest causes of cancer deaths. Having a family history of colon cancer or certain genetic syndromes increases a person’s risk of being diagnosed with colon cancer and other types of cancer. Genetic mutations in DNA can allow parents to pass risky genes on to their children. Luckily, not everyone with these gene mutations will go on to develop colon cancer. Early and frequent screening can catch cancer while it’s most likely treatable. Ask your doctor when you should get checked. Get checked for you, get checked for your family. Then CheckIt4Andretti!
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