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Several factors can increase your risk for colon cancer. Genetics is one of them.
“Colon cancer is the third most common cancer among Americans. It occurs when an abnormal growth of tissues called polyps turn into cancerous cells,” says Dr. Rizza Mira.
According to the American Cancer Society (ACS), one in every three people with colorectal cancer has at least one family member with the same condition.1
People with a family history of colon cancer have a higher risk of developing this condition. This risk increases further if:1
While colon cancer can run in the family, only five to six percent of colon cancers are linked to gene mutations inherited from parents.2
Ninety-five percent of colorectal cancers are sporadic. This means they are caused by genetic changes that you develop, not inherit.2
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Colon cancer is a type of cancer that affects the colon. It’s sometimes called rectal cancer or colorectal cancer, depending on the affected area:
Not including skin cancer, colorectal cancers are the third most diagnosed cancer in the United States.3
Based on current trends, the ACS anticipates around 151,000 new cases of colon and rectal cancer in the U.S. by 2022.3
People with colon cancer may not show early signs, but symptoms will start to appear once the disease worsens. The progression of colon cancer will also depend on the stage and invasiveness of the tumor.
Symptoms may also vary depending on the number and size of the cancer tumors and where they are located in the intestinal tract. Some symptoms also result from where the cancer cells spread, the liver, for example.
In general, a person with colon cancer will experience changes in bowel movement, such as passing stool more or less often than usual.
The consistency and appearance of your stool will also change. They might become watery (like in diarrhea), hard (constipation), or narrow.
Other signs and symptoms of colon cancer include:
The exact cause of colon cancer isn’t known. But experts believe it starts with mutated genes that alter certain DNA within the cells of your colon. Some environmental factors and unhealthy lifestyle habits also increase the risk.
Each cell in your body contains deoxyribonucleic acid or DNA. DNA holds instructions for your cells, so they’ll know what to do.
Some of these cells divide and grow to maintain the colon’s function. But when the DNA in these cells is damaged, they’ll continue to reproduce even if they’re not needed.
This abnormal cell growth causes the formation of benign (noncancerous) tumors called polyps. Over time, these polyps will grow in size and in number.
Scientists believe that colon cancer develops from adenomatous (precancerous) polyps. The mutations that eventually lead to it can be acquired or inherited.
When one or both parents inherit or develop gene mutations, they can pass them on to their children during conception. These are inherited mutated genes.
“Mutated genes may remain silent for a long time. Some triggering factors may activate them,” says Dr. Mira.
Certain mutations increase your risk for colon cancer, such as:1
The higher risk associated with family isn’t clearly understood. It may be caused by inherited genes, shared environmental factors, or both.1
For example, a family whose diet consists mainly of processed meats places its members at risk for colorectal cancer.
Most colorectal cancers are caused by acquired gene mutations, not inherited genes. These are mutations that develop later in life after a person is born.4
The risk of acquiring mutated genes increases with age. Certain lifestyles and environmental factors can trigger these genetic changes and lead to cancer.5
Several risk factors have been linked to colon cancer. Having one or more of them doesn’t mean you’ll get the disease, but they can increase your chances.
Some of these risk factors are modifiable, which means you can change them. Non-modifiable factors are those you can’t do anything about.
Some known risk factors linked to colon cancer include:
Having a diet rich in red meats (e.g., pork, beef, and lamb) and processed meats (e.g., hot dogs and canned meats) is also considered a risk factor.1,6
Other studies show that a typical Western diet, which is high in fat and calories but low in fiber, raises your risk of developing colorectal cancer.6
Anyone can develop colon cancer regardless of age, gender, and race.
“Screening for colon cancer plays a very important role in prevention. The U.S. Preventive Services Task Force advises that adults 45 to 75 years of age undergo screening colonoscopy,” says Dr. Mira.
However, men have a slightly higher risk of colorectal cancer than women. In the U.S., it’s also more common in African Americans and people over 50.2
Ashkenazi Jews or Jews of Eastern European descent have a very high risk compared to other ethnic groups in the world.1
A family history of colorectal cancer and polyps (especially in first-degree relatives) put you at risk of developing colon cancer.1,2
Having the following conditions may also increase your risk:
Polyps are not cancerous, but they can lead to colon cancer over time. The risk is greater if the adenomas are large and if there are many of them.2
“Screening tests for colon cancer are geared towards finding polyps along the GI tract. Screening methods include occult blood (hidden blood in stools), sigmoidoscopy, and colonoscopy,” says Dr. Mira.
Even if you have them removed, there’s still a risk for additional polyp growth and eventual colon cancer.2
If you were previously treated for colorectal cancer, there’s a chance that new cancers will develop in other parts of your colon and rectum.1
People diagnosed with ovarian or uterine cancer also have a higher risk of colon cancer.2 Colon cancers can also arise as metastatic spread from other cancer origins.
It’s not fully understood how this happens, but cancer can recur after treatment (cancer recurrence) and spread to other parts of the body (metastasis).7
Having certain genetic mutations and lifestyles (such as smoking and poor diet), can also trigger other cancers (or second cancers) to develop after the first.8
Inflammatory bowel diseases (IBD) like Crohn’s disease and ulcerative colitis cause chronic inflammation in the colon. Left untreated, this leads to dysplasia.
Dysplasia is when the cells lining your colon or rectum look abnormal. While not cancerous, they can eventually develop into cancer.1
People with type 2 diabetes are more likely to develop colorectal cancer.1
Researchers don’t know exactly why this is. But it does share some risk factors with colon cancer, like being overweight or obese and physical inactivity.
About five percent of people with colorectal have inherited mutations that cause family cancer syndromes or cancers seen in families.2
Having any hereditary cancer syndrome raises your chances of developing cancer of the colon as well as other cancers. Below are some of these syndromes:
People with FAP usually develop hundreds to thousands of pre-cancerous colorectal polyps. Without treatment, this leads to colon or rectal cancer.1
FAP causes one percent of all colorectal cancers. There are three types:
Also known as hereditary nonpolyposis colorectal cancer (HNPCC), Lynch syndrome causes two to four percent of all colorectal cancers.1
People who have it tend to have few colon polyps. They can also have a fifty percent lifetime risk for colon cancer, depending on the affected genes.1
Turcot and Muir-Torre syndrome are both subtypes of HNPCC.
Those that have both Lynch and Turcot syndrome have a higher risk for colorectal cancer and glioblastoma, a type of brain cancer.1
Rare genetic diseases like Peutz Jeghers syndrome (PJS) and MUTYH-associated polyposis (MAP) are both linked to familial colon cancer:1
Hamartomas are noncancerous polyps, just like adenomas. However, on an estimate, a person with PJS can have a 40% chance of developing cancer. While an adenoma resembles a gland, a hamartoma looks like disorganized tissue.
A family history of colorectal cancer can double your risk of developing this disease.2 You should tell your doctor if one or more relatives have it.
To diagnose or prevent colorectal cancer, your doctor might:
If you’re not sure, you can visit a genetic counselor and take a DNA test. Genetic testing can check for mutated genes that increase your risk for colorectal cancer.
Genetic counselors may also suggest DNA testing to see which family members have the same risk, so they can be screened for the disease.
Early screening is important because treatments are more likely to succeed if you have fewer and smaller adenomas or if your colon cancer is in its early stages.
At-home colon cancer tests offer a convenient way of finding out. You can take these tests at home and get results in as little as a few minutes to a week.
Most of these kits are fecal immunochemical tests (FIT), similar to those ordered by doctors. They check stool samples for microscopic blood. Screening using fecal occult blood is recommended yearly.
The presence of blood in stool may be a sign of polyps or colon cancer. However, it can also be caused by hemorrhoids, IBD, and stomach ulcers. This warrants additional testing like colonoscopies to see the colon.
If you’re positive for microscopic blood—or blood that’s invisible to the naked eye—you can take your results to a doctor so they can diagnose your condition.
The doctor may perform stool tests and visual exams, such as:9
A colonoscopy is still the gold standard for colon cancer screening. Doctors use it to check for unusual growths, including polyps and tumors.
If there’s abnormal tissue, your doctor can remove them during the procedure and send it for a biopsy. Removing polyps may help with colon cancer prevention.
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