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Colorectal Cancer
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Digestive System

Colorectal Cancer

Colorectal cancer develops in the tissues of the colon or rectum, and regular screening is essential for early detection and treatment.

What is colorectal cancer?

Colorectal cancer is cancer that develops in the tissues of the colon or rectum. Your colon and rectum are part of your digestive system:

  • Colon: The first and longest part of your large intestine. It absorbs water and some nutrients from foods and changes leftover waste products into stool.
  • Rectum: The lower part of your large intestine where your body stores stool.

Cancer that begins in the colon is called colon cancer, and cancer that begins in the rectum is called rectal cancer.

Causes & Risk Factors

Colorectal cancer happens when there are changes in your genetic material (DNA), known as mutations or variants. While some genetic changes are inherited, others occur during your lifetime. Other factors that increase your risk include:

  • Being older
  • Personal or family history of colorectal cancer
  • History of adenomas (colorectal polyps that are 1 centimeter or larger or look abnormal)
  • Genetic syndromes such as familial adenomatous polyposis (FAP) or Lynch syndrome
  • Chronic ulcerative colitis or Crohn disease for 8 years or more
  • Consuming three or more alcoholic drinks per day
  • Smoking cigarettes
  • Being Black
  • Obesity

Symptoms

Colorectal cancer may not always cause symptoms, especially at first. If you do have symptoms, they could include:

  • A change in bowel habits lasting more than a few days (diarrhea, constipation, feeling that the bowel does not empty completely, or stool that is narrower or a different shape than usual)
  • Blood in the stool
  • Frequent gas pains, bloating, fullness, or cramps
  • Unexplained weight loss
  • Fatigue

Screening & Diagnosis

Because colorectal cancer may not cause symptoms at first, screening is vital. Most experts recommend starting screenings at age 45 and continuing until at least age 75. Tests include stool tests, colonoscopies, and flexible sigmoidoscopy.

If symptoms exist or screening results are abnormal, diagnostic tests may include a physical exam, a digital rectal exam, biopsy, or other blood and tissue tests.

Treatment & Management

Treatment depends on age, general health, and the type of cancer. Options for colon cancer include surgery, radiofrequency ablation, cryosurgery, chemotherapy, radiation therapy, targeted therapy, and immunotherapy. Options for rectal cancer include surgery, radiation therapy, chemotherapy, active surveillance, targeted therapy, and immunotherapy.

Prevention

You can take steps to reduce your risk by not smoking, limiting alcohol, managing your weight, exercising regularly, getting regular screenings, and having polyps removed before they become cancerous.

Frequently Asked Questions

No, you should not stop eating fiber before a colonoscopy. In fact, a low-residue or clear liquid diet is typically required for the 1 to 3 days leading up to the procedure to ensure the bowel is completely empty for clear visualization. Fiber is beneficial for long-term colon health and reducing cancer risk, but it must be eliminated temporarily before screening to prevent residue from obscuring the view of the colon lining.
Yes, it is possible to develop colorectal cancer even after a normal colonoscopy, although the risk is significantly lower for several years. Polyps can develop quickly, or a small polyp may have been missed during the initial exam. However, a normal result generally provides protection for about 5 to 10 years, so it is crucial to adhere to your doctor's recommended follow-up interval rather than assuming you are immune to the disease indefinitely.
You should seek immediate medical attention if you experience visible bright red or dark tarry blood in your stool, severe abdominal pain that does not resolve, unexplained weight loss of more than 10 pounds in a short period, or a persistent change in bowel habits such as new-onset constipation or diarrhea lasting more than a few days. These symptoms may indicate a blockage, significant bleeding, or advanced disease that requires urgent evaluation rather than routine screening.
If you have a first-degree relative (parent, sibling, or child) diagnosed with colorectal cancer or advanced adenomas, your screening should begin at age 40 or 10 years before the age of the youngest affected relative, whichever comes first. For those with specific genetic syndromes like Lynch syndrome or Familial Adenomatous Polyposis, screening often begins in early adulthood (teens or 20s) and requires more frequent colonoscopies, such as every one to two years, due to the significantly higher risk of rapid polyp development and cancer.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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