Colon cancer begins in the colon, which is part of the large intestine. The large intestine plays a vital role in the digestive system, helping to absorb nutrients and water from food.

This type of cancer most often affects older adults, though it can occur at any age. It usually starts as polyps (small clumps of cells) in the colon. Although polyps are typically non-cancerous, some can eventually develop into colon cancer.

Polyps usually do not show symptoms, making it important for individuals to undergo regular screening tests to identify and remove them, which can help prevent colon cancer from developing.

When colon cancer does appear, several treatment options, such as surgery, radiation therapy, and medications (including chemotherapy, targeted therapy, and immunotherapy), can help manage the disease.

Colon cancer is sometimes referred to as colorectal cancer, which includes both colon cancer and rectal cancer (cancer of the rectum).

Most colorectal cancers come from precancerous polyps — adenomatous polyps or serrated polyps — that form over a number of years (5 to 10) to become a cancer. A polyp is a mushroom-like or flat growth on the inside wall of the colon or rectum. Polyps grow slowly over many years. 

Not all colon polyps have the same risk of turning into colon cancer. Precancerous polyps could become cancerous; other types of polyps (hyperplastic, inflammatory) do not.

Removing precancerous polyps before they turn into cancer prevents colorectal cancer. If caught early before any symptoms arise, surgery can cure colorectal cancer. Finding colorectal cancer early leads to easier treatments and higher survival rates.

Symptoms

Colon cancer may not show symptoms in its early stages. However, as the cancer progresses, symptoms may vary depending on its size and location in the colon. Symptoms include:

• Changes in bowel habits (more frequent diarrhea or constipation)

  
  

• Rectal bleeding or blood in the stool

  
  

• Abdominal discomfort (cramps, gas, pain)

  
  

• Feeling of incomplete bowel movement

  
  

• Weakness or fatigue

  
  

• Unexplained weight loss

When to Seek Medical Attention

If you experience persistent symptoms that concern you, consult a healthcare provider for further evaluation.

Causes

The exact cause of colon cancer remains unclear, but it is generally linked to changes in the DNA of colon cells, which causes them to multiply abnormally and form tumors. These changes disrupt the normal life cycle of cells, allowing them to survive longer than healthy cells.

Over time, these cells can invade healthy tissues and spread to other parts of the body (metastasis).

Risk Factors

Several factors may increase the risk of developing colon cancer, including:

• Older age: Most people with colon cancer are over 50, though cases in younger individuals are rising.

  
  

• Ethnicity: Black people have a higher risk of colon cancer.

  
  

• Personal history: A previous history of colorectal cancer or polyps increases the risk.

  
  

• Inflammatory bowel diseases: Conditions like ulcerative colitis or Crohn's disease raise the risk.

  
  

• Genetic syndromes: Conditions such as familial adenomatous polyposis and Lynch syndrome can increase risk.

  
  

• Family history: A family member with colon cancer increases your risk.

  
  

• Diet: A diet high in fat and low in fiber may increase the risk. Red meat and processed meats are also linked to a higher risk.

  
  

• Physical inactivity: A lack of regular exercise may contribute to an increased risk.

  
  

• Obesity: Being overweight raises both the risk of colon cancer and mortality from it.

  
  

• Diabetes: Those with diabetes or insulin resistance face a higher risk.

  
  

• Smoking and alcohol: Smoking and excessive drinking can both raise the risk of colon cancer.

  
  

• Radiation therapy: Previous radiation treatment to the abdomen can increase the risk.

Prevention

• Screening: Regular screening for colon cancer, starting at age 45 for individuals with average risk, can help detect early signs of the disease. For those with increased risk (e.g., family history), screening should begin earlier.

• Lifestyle Changes:

  
  

  • Eat a variety of fruits, vegetables, and whole grains for fiber and antioxidants.

    
    

  • Limit alcohol consumption.

    
    

  • Quit smoking with the help of your healthcare team.

    
    

  • Exercise regularly, aiming for at least 30 minutes most days of the week.

    
    

  • Maintain a healthy weight through diet and physical activity.

Prevention for High-Risk Individuals

In certain cases, medications like aspirin or aspirin-like drugs may reduce the risk of colon cancer for those at high risk. However, this approach is typically not recommended for people with average risk due to potential side effects, such as ulcers or gastrointestinal bleeding.

If you're at higher risk for colon cancer, consult with your healthcare team to assess whether preventive medication is suitable for you.

More Information

• Colon cancer screening options

  
  

• The age at which you can stop screening

Important Reminder: This information is intended only to provide general guidance. It does not provide definitive medical advice. It is very important that you consult your doctor about your specific condition.

Colorectal cancer (CRC) - AGA GI Patient Center