If you have colorectal cancer (or know someone who does), you might be wondering, why me? That’s a great question, and one that researchers are exploring at this very minute. Because while we have some understanding of who is at risk for the disease, there’s still a lot we don’t know. Let’s take a look at where things currently stand when it comes to the cause of colon cancer.
We went to some of the nation's top experts in colorectal cancer to bring you the most up-to-date information possible.
Leonid Cherkassky, M.D.Assistant Professor of Oncology
Gautam Mankaney, M.D.Gastroenterologist
Eduardo Vilar-Sanchez, M.D., Ph.D.Associate Professor of Clinical Cancer Prevention
What Is Colorectal Cancer Again?
Colorectal cancer, often referred to as just colon cancer, is a disease that can affect both your colon and rectum.
You might not have heard a ton about colorectal cancer, but every year, it kills more people than breast or prostate cancer. In fact, it’s the second most common cause of cancer deaths among men and women combined in the United States, after lung cancer.
The number one cause of colon cancer is getting older—90% of cases are diagnosed in people over age 50. Obesity, family history, and genetic disposition are other causes.
Experts know a lot about what causes colon cancer—and not enough. They generally can’t predict exactly when or where a tumor will develop, or why one person gets it but not another. But they can rattle off a long list of factors that set the stage and make it more likely that a cancer will develop.
But before we get to individual risk factors, there’s one overarching reason that colorectal cancer happens at all: Location.
When it comes to cancer, the colon is just in a bad neighborhood. In fact, experts say that the colon and rectum, which together make up the large intestine, accounted for about 145,000 cases of cancer in 2019, compared to less than 11,000 cases of cancer of the small intestine. That’s a 13-fold difference—which is even more striking when you take in account the fact that the small intestine is about four times longer than the large intestine.
So what is it about the colon that makes it so cancer-prone?
Start with the fact that it’s the end of the line for the digestive system—a waiting area where waste products sit before being shown the door, as it were. It works like this:
All the good stuff has been pulled out of the food you ate and used to nourish your body.
What’s left contains are the unwanted byproducts, like potentially dangerous chemicals produced when meat is cooked at high temperatures.
When the colon does its job of removing water from that unsavory mishmash and preparing it to be excreted, those toxic compounds sit right up against the intestinal lining.
Meanwhile, the cells in the lining are especially fast-dividing (they’re speedy enough to create a whole new lining every week).
A cell’s DNA has to be copied every time it divides, and occasionally a mistake will be made; the fact that colon cells divide rapidly means more opportunities for error. If enough mistakes accumulate, the cell’s normal controls on growth get lost and it starts to divide in an out-of-control way.
And there you are: Colon, meet cancer.
Colorectal Cancer Risk Factors
Beyond those universal risk factors (eating food and owning a colon), there are plenty of other elements that may make colon cancer more likely for certain people. These are a few variables that could raise your risk.
Simply getting older is the most significant risk factor for colon cancer, because with every round of cell division, DNA has a chance to mutate. Those possible mutations start to accumulate and become noticed in various forms around age 50, when the rate of colon cancer begins creeping up. The average age at diagnosis is 68 for men and 72 for women.
If your mom, dad, brother or sister, or child has colon cancer, it could indicate an inherited gene mutation that increases the risk of the disease. It could also simply reflect shared habits that are bad for colon health. In either case, a family history of the disease means you have nearly double the chance of developing colon cancer yourself.
If you’ve had colon cancer already, you’re at higher risk of developing it again. Your risk also increases if you’ve previously had a kind of polyp in your colon known to become cancerous, like an adenoma. (Polyps, or clusters of cells that create extra tissue, can be found during a colonoscopy.)
Several inherited conditions increase the odds of developing colon cancer because of a genetic defect that’s passed from parent to child. While serious, these disorders are rare, accounting for only about 5% of overall cases.
Lynch syndrome: People with this condition inherit a corrupt or mutated version of genes that are responsible for correcting errors in the genetic code. Without this error-correcting ability, DNA errors multiply, causing cancer risk to spike.
In fact, Lynch syndrome, also called hereditary nonpolyposis colorectal cancer (HPCC), is the most common cause of hereditary colorectal or colon cancer, causing about 4,000 cases of colon cancer each year. (Lynch syndrome also increases the risk of cancer of the uterus, stomach, liver, kidney, brain, and skin.)
Familial Adenomatous Polyposis (FAP): This rare, inherited condition is caused by a defect in the adenomatous polyposis coli (APC) gene that results in extra tissue, or polyps, to form in your colon and rectum, raising the risk of cancer. People with FAP can start developing polyps by their teenage years—cancer is almost inevitable unless the colon is removed.
Inflammatory Bowel Disease
People with inflammatory bowel disease (IBD), such as Crohn’s disease or ulcerative colitis, are at higher risk of colon cancer, probably because the disease causes chronic inflammation of the large intestine. (Persistent inflammation can damage DNA.) That can lead to dysplasia—cells that aren’t cancerous but that are clearly abnormal and at heightened risk of becoming cancerous.
If you have IBD, you may need to be screened more frequently for colon cancer—in some cases, doctors may recommend getting a colonoscopy every year or so. (Helpful clarification: Irritable bowel syndrome, or IBS, sounds similar to IBD and shares some symptoms but doesn’t raise the risk of colon cancer.)
Some dangers of drinking too much are obvious: You’re more likely to get into an accident if you drive drunk, and mixing alcohol with drugs (prescription or otherwise), raises the risk of a bad interaction.
But alcohol’s role in cancer tends to be overlooked. Here are the facts: Having more than about two alcoholic drinks a day if you’re a man and more than one a day if you’re a woman raises the risk of colon cancer by about 40%. (Drinking is also linked to breast, mouth, throat, esophagus, and liver cancers.)
Alcohol causes trouble in a number of ways. For one thing, it’s broken down into a compound called acetaldehyde—a chemical that is known to damage DNA. Alcohol consumption can also cause chronic inflammation, a problem for colon cells.
While smoking is best known for its impact on the risk of lung cancer and heart disease, it also increases the risk of additional cancers, from one end of your body (mouth) to the other (colon and rectum). One study of twins found that long-term heavy smokers were about three times more likely to develop colon cancer than their non-smoking sibling.
People who are obese are about 30% more likely to develop colorectal cancer, according to the National Cancer Institute. The reason isn’t yet understood, but scientists think several factors may be at play, including the fact that obesity can cause low-level but chronic inflammation throughout the body.
Although the reasons why are still being studied, in the United States, African Americans are more likely than any other ethnic group to develop, and to die from, colon cancer. Jews of Eastern European descent (Ashkenazi Jews) are also at increased risk—in fact, their risk is among the highest found for any ethnic group in the world.
Bad news, good news: While desk jockey jobs—or any other reason you sit around all day—is a risk raiser for colorectal cancer, being physically active helps protect against the disease. The possible reason? Exercise reduces inflammation and lowers the level of hormones like insulin and estrogen that may encourage the development of cancer.
You may also have noticed that exercise speeds up the time it takes to process the food you eat. More efficiency in the pooping department decreases the amount of time your GI tract is exposed to potential carcinogens, lowering cancer risks.
Most researchers believe that a diet big on red meat or processed meat (see: hot dogs and cold cuts) raises the risk of colon cancer. In addition, cooking meat at high temps (think pan-frying or grilling over open flames) creates chemicals called heterocyclic amines and polycyclic aromatic hydrocarbons, which scientists strongly suspect can trigger DNA mutations.
Of course, just because you have a family history of the disease or have been diagnosed with IBD doesn’t automatically mean you’ll get colorectal cancer. But if you’re worried, take a look at the variables you can control, like what you eat and drink, and think about making positive changes in your life. You won’t just be lowering your risk of colon cancer, you’ll be raising your odds of good health for the years to come.
Frequently Asked QuestionsColorectal Cancer Causes
Can taking aspirin cut my risk of colon cancer?
Taking an aspirin a day for 10 to 20 years cuts the risk of colon cancer by 40%, according to a review by the United States Preventive Services Task Force. Unfortunately, taking a daily aspirin also ups the risk of gastrointestinal bleeding and certain kinds of stroke, so you should talk to your doctor about how the potential risks and benefits net out for you.
Does taking calcium reduce the risk of colorectal cancer?
This is an open question. Some studies suggest that people who take calcium supplements—or eat a lot of dairy, which typically is a good source of calcium—are less likely to develop colon cancer. The National Cancer Institute is still evaluating the evidence, but in the meantime, there’s little downside to boning up.
How does hormone replacement therapy affect colon cancer risk?
Taking estrogen plus progestin hormone therapy after menopause may cut the risk of invasive colon cancer, according to recent studies. On the flip side, hormone therapy increases your risk of breast cancer, so talk with your doctor about what makes the most sense for you.
I’m at high risk of colon cancer. When should I start getting screened?
If you have a family history—say your mother, father, sibling, or child has had the disease—you should get your first colonoscopy at age 40, or 10 years earlier than the earliest diagnosis among your relatives. Experts suggest that African-Americans be screened starting at age 45.
Aspirin and Colorectal Cancer:Annals of Internal Medicine. (2016). “Aspirin for the Prevention of Cancer Incidence and Mortality: Systematic Evidence Reviews for the U.S. Preventive Services Task Force.” ncbi.nlm.nih.gov/pubmed/27064482?dopt=Abstract