Colon cancer and genetics

Colon cancer, also known as colorectal cancer, is the fourth most common form of cancer among adults in the U.S. This cancer starts in your colon (large intestine) or rectum (the end of your large intestine).

Having a family history of colon cancer increases your risk. But there are other risk factors to consider too. Here’s what you should know about colon cancer and genetics — and whether you should have colon cancer genetic testing.

Is Colon Cancer Hereditary?

Most of the time, colon cancer happens in people who don’t have a family history. But about one in three people who develop colon cancer do have it in their family. Researchers believe there is a link between colon cancer and genetics, but your genes don’t guarantee you’ll develop cancer.

If you have a family history of colon cancer, learn who has had it and how old they were at diagnosis. That can help determine your risk. You might have a higher risk if you have:

  • One or more first-degree relatives (a parent, sibling, or child) who have had colon cancer.
  • A first-degree relative diagnosed before the age of 50
  • Family members who have had adenomatous polyps, a kind of polyp that can turn into cancer.
  • African American race, or Ashkenazi Jewish ethnicity. These groups are at much higher risk.

When cancer runs in families, it might be partly because of genes. Or it might be because of other risk factors family members share, like environment or diet.

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Other Colon Cancer Risk Factors

Colon cancer is primarily linked to lifestyle factors. That’s good news because you can control or change your lifestyle. If colon cancer runs in your family, it’s crucial to look out for and try to reduce these risk factors:

  • Being overweight (BMI 25.0-29.9) or obese (BMI greater than 30).
  • Having a sedentary lifestyle.
  • Eating lots of processed meats like bacon, sausages, hot dogs, and cold cuts like salami, or bologna. A diet high in red meat like steak or burgers also increases your risk.
  • Not eating enough fiber-rich foods like fruits, vegetables, whole grains, or beans.
  • Having low levels of vitamin D. Ask your doctor if you should take a supplement.
  • Drinking excess alcohol. Limit it to no more than two drinks a day for men and one drink for women if you do drink.
  • Smoking. This doesn’t just affect your lungs. It also increases your risk of colon cancer.

Other things that increase your risk of colon cancer but are out of your control include:

  • Your age. Your risk increases as you age.
  • A previous personal history of adenomatous polyps or colon cancer.
  • Having inflammatory bowel disease like Crohn’s or colitis.
  • Having type 2 diabetes. Managing your blood sugar helps, but people with diabetes still have a higher risk.

Colon Cancer Genetic Testing

Many people wonder about colon cancer genetic testing as a way to determine your risk. If this cancer runs in your family, you can ask your doctor about genetic testing. It’s not right for everyone, but they might recommend it if you:

  • Have a first-degree relative who developed colon cancer before the age of 50.
  • Developed more than 10 adenomatous polyps during your lifetime.
  • Have family members with known genetic conditions linked to colon cancer.

Genetic testing won’t give you all the answers, but it will tell you if you carry genetic mutations that increase your risk. Only about 5% of people who develop colon cancer have genetic mutations that increase their risk of developing the disease.

You can’t inherit colon cancer, but you can inherit a mutated gene that causes certain family cancer syndromes.

Family cancer syndromes are clusters of symptoms that, over time, might lead to cancer. The two most common inherited family cancer syndromes are:

  • Lynch syndrome. This accounts for 2% to 4% of colon cancers. People with Lynch syndrome are more likely to develop colon cancer before 50.
  • Familial adenomatous polyposis (FAP). FAP causes about 1% of colon cancer cases. People with FAP have hundreds or thousands of polyps in their colon and rectum. Cancer can develop as young as age 20.

In addition to colon cancer, family cancer syndromes can increase the risk of developing these other types of cancer:

  • Breast
  • Uterine (endometrial)
  • Ovarian
  • Prostate
  • Stomach

If you have a strong family history of these other cancers, ask your doctor about genetic testing.

How to Reduce Your Risk

Colon cancer deaths have been declining because many people make significant lifestyle changes to lower their risk. The following lifestyle changes can help reduce everyone’s risk — and they’re vital if colon cancer runs in your family:

  • Lose excess weight.
  • Get regular exercise.
  • Quit smoking.
  • Drink alcohol only in moderation.
  • Cut back on red and processed meat.
  • Eat more fruits, vegetables, beans, and whole grains.

Talk to your doctor about your family history and other risk factors — and make sure you get screened as recommended. If colon cancer runs in your family, you’ll have a much better chance of catching it early with regular colonoscopies.

American Cancer Society. Colorectal Cancer. LINK

British Journal of Surgery. Risk of colorectal cancer associated with BRCA1 and/or BRCA2 mutation carriers: systematic review and meta-analysis. LINK

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