Colon cancer is a disease that begins in the large intestine when cells start growing out of control, often developing from small growths called polyps that form on the inner lining of the colon.

The colon, also known as the large intestine, is a vital part of your digestive system. It stretches about five feet long and works hard every day to help your body absorb water and nutrients from the food you eat. The colon connects to the rectum and eventually the anus, creating the pathway through which waste leaves your body. When cancer develops in this part of your body, it usually starts quietly, often without causing any noticeable problems at first.^[1][2]

How Does Colon Cancer Develop?

Your colon wall is made up of several layers, including mucous membrane, tissue, and muscle. The innermost lining, called the mucosa, contains cells that produce and release mucus and other fluids. When these cells change or mutate, they may form a small clump of cells called a polyp. Not all polyps are dangerous, but some types can gradually transform into cancer over time.^[2]

The journey from a normal polyp to cancer is usually a slow one. Medical experts have found that it typically takes about ten years for a colon polyp to develop into cancer. This long timeline is actually good news because it gives doctors plenty of opportunity to find and remove polyps before they become dangerous. If polyps are not found and removed, the cancer can work its way through the layers of your colon, spreading into surrounding tissue and muscle. Eventually, it may travel to other parts of your body through your lymph nodes or blood vessels.^[2]

Who Gets Colon Cancer? Understanding the Numbers

Colon cancer is one of the most common types of cancer in the United States. According to health authorities, it ranks as the third most frequently diagnosed cancer in Americans. When looking at cancer-related deaths, colon cancer is the second leading cause, with more than 50,000 Americans dying from the disease each year. This means that nearly 140 people lose their lives to colon cancer every single day.^[6]

Looking at the bigger picture worldwide, colon cancer accounts for approximately ten percent of all cancer cases globally. In 2020, health experts estimated that more than 1.9 million new cases of colorectal cancer occurred around the world, with over 930,000 deaths from the disease. The rates vary significantly depending on where people live. The highest rates of colon cancer are found in Europe, Australia, and New Zealand, while Eastern Europe has particularly high mortality rates.^[9]

The disease affects both men and women, though men are slightly more likely to develop it. Among different racial and ethnic groups, Black Americans face a higher risk of colon cancer compared to people of other backgrounds. The disease traditionally affects older adults, with most cases occurring in people over the age of fifty.^[2][11]

What Causes Colon Cancer?

The exact cause of colon cancer remains unclear to scientists. However, they know that the disease develops when certain changes occur in the DNA (the genetic material inside cells) of colon cells. These changes cause the cells to grow and divide in abnormal ways. Unlike normal cells that have a regular life cycle, cancer cells keep multiplying without control and don’t die when they should.^[3]

While we don’t fully understand what triggers these initial cell changes, researchers have identified many factors that increase the likelihood of developing colon cancer. These are called risk factors, and understanding them can help people make choices that might lower their chances of getting the disease.^[4]

Who Is at Higher Risk?

Several factors can increase a person’s risk of developing colon cancer. Having one or more risk factors doesn’t mean you will definitely get the disease, but it does mean your chances are higher than someone without these factors. On the other hand, some people develop colon cancer even without any known risk factors.^[13]

Family history plays a significant role in colon cancer risk. If you have a parent, sibling, or child who has had colon or rectal cancer, your risk increases by two to five times compared to someone without this family connection. Some families inherit specific genetic changes that can make their risk of colon cancer extremely high, sometimes approaching 100%. These inherited conditions include familial adenomatous polyposis (FAP) and Lynch syndrome (also called hereditary nonpolyposis colorectal cancer). Genetic testing may be recommended for families where multiple members have had colon cancer or other related cancers, or where relatives were diagnosed at a young age.^[6][13]

Your personal medical history also matters. If you’ve previously had colon, rectal, or ovarian cancer, you face a higher risk of developing colon cancer again. Additionally, if you’ve had large polyps (growths that are one centimeter or bigger) or polyps with abnormal-looking cells, your risk increases. People with chronic inflammatory bowel conditions like ulcerative colitis or Crohn disease that they’ve had for eight years or longer also face elevated risk.^[13]

Lifestyle choices significantly impact colon cancer risk. Smoking cigarettes increases your chances of developing the disease. Drinking three or more alcoholic beverages per day also raises risk. Being overweight or obese contributes to higher colon cancer rates. Your age is another important factor, as the risk of colon cancer increases as you get older.^[13]

Recognizing the Warning Signs

One of the challenges with colon cancer is that many people don’t experience any symptoms in the early stages. This is why screening tests are so important—they can find cancer before symptoms appear. When symptoms do develop, they often resemble problems caused by less serious conditions, which can make it difficult for people to know when something is wrong.^[1][2]

Blood in or on your stool is one of the most common symptoms of colon cancer. You might see bright red blood on the toilet paper after wiping, notice blood in the toilet bowl, or observe that your stool looks dark, tarry, or brick red. It’s important to remember that blood in your stool doesn’t automatically mean you have cancer. Many other conditions, from hemorrhoids to small tears in the anal area, can cause bleeding. Even eating certain foods like beets can change your stool’s color. However, if you notice blood in your stool, it’s always best to check with a healthcare provider.^[2][7]

Changes in your bowel habits can also signal a problem. If you experience ongoing constipation or diarrhea that doesn’t go away, or if you feel like you still need to go to the bathroom even after you’ve just been, you should talk to a doctor. Some people notice that their stools become narrower than usual. These changes might come and go or stay constant.^[2][7]

Abdominal pain or discomfort is another warning sign. While many things can cause belly pain, if you have pain that has no clear cause, doesn’t go away, or hurts a lot, it’s worth getting checked by a healthcare provider. Similarly, if your stomach feels bloated and this sensation lasts for more than a week or gets worse, you should seek medical advice.^[2][11]

Other symptoms that may appear include unexplained weight loss, persistent fatigue or weakness, and low iron levels in your blood. Some people with colon cancer feel completely healthy, especially in the early stages, which is why screening is so crucial.^[6][7]

Can You Prevent Colon Cancer?

Colon cancer stands out as one of the most preventable types of cancer. Unlike many other cancers, doctors have effective ways to stop colon cancer before it even starts. The key to prevention lies in finding and removing polyps before they turn cancerous.^[6]

Screening tests are your best defense against colon cancer. These tests can detect polyps in your colon, and doctors can remove them during the same procedure. Once the polyps are gone, they can’t develop into cancer. Screening can also find cancer in its earliest stages, when treatment is most effective and survival rates are highest. Medical experts recommend that people at average risk should begin screening at age 45. If you have a family history of colon cancer or other risk factors, your doctor may recommend starting screening even earlier.^[5][6]

Colonoscopy is considered the most effective screening method. During this procedure, a doctor uses a long, flexible tube with a tiny camera attached to examine your entire colon. If they spot any polyps, they can remove them right away. Studies show that colonoscopy with polyp removal can reduce cancer risk by up to 90%. Since screening colonoscopy became more common, cancer rates have dropped by 30%.^[6]

Lifestyle choices also play a crucial role in prevention. Eating a healthy diet rich in fruits, vegetables, and whole grains while limiting red and processed meats may help reduce your risk. A high intake of processed meats has been shown to increase colon cancer risk, while a diet full of plant-based foods appears protective.^[9][20]

Staying physically active has been linked to lower colon cancer rates. You don’t need to become an athlete—even moderate regular exercise can make a difference. Maintaining a healthy body weight is also important, as obesity increases colon cancer risk. If you smoke, quitting is one of the best things you can do for your overall health, including lowering your cancer risk. Limiting alcohol consumption to moderate levels also helps, as heavy drinking may increase your chances of developing the disease.^[9][20]

What Happens in Your Body During Colon Cancer

Understanding what happens inside your body when colon cancer develops can help make sense of symptoms and treatments. The process begins in the mucosa, the innermost layer of your colon. This layer is made up of cells that normally produce mucus and other fluids to help your digestive system work smoothly.^[2]

When certain cells in the mucosa undergo changes or mutations, they may begin forming small growths called polyps. These polyps can be flat or have a stalk, like a mushroom. While most polyps remain harmless, certain types called adenomas have the potential to become cancerous. The transformation from a normal polyp to cancer happens gradually, usually over many years.^[3][5]

As cancer develops, it starts to invade deeper layers of the colon wall. The colon wall consists of multiple layers: the inner mucosa, a layer of connective tissue, layers of muscle, and an outer protective layer. Cancer that stays in the inner layers is considered early-stage and is often easier to treat. As it grows through more layers, it becomes more advanced and potentially more dangerous.^[2]

If left untreated, colon cancer can spread beyond the colon itself. It may extend into nearby lymph nodes, which are small bean-shaped structures that are part of your immune system. Cancer cells can also enter blood vessels and travel to distant parts of the body, a process called metastasis. The most common places for colon cancer to spread are the liver and lungs.^[2]

As cancer grows, it can interfere with the normal function of your colon. The right side of your colon primarily absorbs water and some nutrients, while the left side mainly stores and helps move waste toward elimination. When cancer develops, it can block the passage of waste, cause bleeding, or prevent proper absorption of nutrients and fluids. These disruptions explain many of the symptoms people experience, such as changes in bowel habits, bleeding, and abdominal discomfort.^[4]

The good news is that thanks to improved screening programs, earlier detection, and better treatments, fewer people are dying from colon cancer than in the past. While the disease remains serious, the outlook continues to improve as medical science advances and more people participate in screening programs.^[2][6]