Colorectal cancer, also called colon cancer or large bowel cancer, includes cancerous growths in the colon, rectum and appendix. With 655,000 deaths worldwide per year, it is the third most common form of cancer and the second leading cause of cancer-related death in the Western world. Many colorectal cancers are thought to arise from adenomatous polyps in the colon. These mushroom-like growths are usually benign, but some may develop into cancer over time. The majority of the time, the diagnosis
of localized colon cancer is through colonoscopy. Therapy is usually through surgery, which in many cases is followed by chemotherapy.

Symptoms

The first symptoms of colon cancer are usually vague, like bleeding, weight loss, and fatigue (tiredness). Local (bowel) symptoms are rare until the tumor has grown to a large size. Generally, the nearer the tumor is to the anus, the more bowel symptoms there will be.

Symptoms and signs are divided into local, constitutional and metastatic.

Local symptoms

• Change in bowel habits
  • Change in frequency (constipation and/or diarrhea),
  • Feeling of incomplete defecation (tenesmus) and reduction in diameter of stool, both characteristic of rectal cancer,
  • Change in the appearance of stools:
    • Bloody stools or rectal bleeding
    • Stools with mucus
    • Black, tar-like stool (melena), more likely related to upper gastrointestinal e.g. stomach or duodenal disease

    Constitutional (systemic) symptoms

    • Unexplained weight loss is a worrying symptom caused by lack of appetite and systemic effects of a malignant growth. However, weight loss is not as much a feature of colorectal cancer as it is of other cancers (e.g. oesophageal carcinoma).
    • Anemia, causing dizziness, fatigue and palpitations. Clinically, there will be pallor and blood tests will confirm the low hemoglobin level.

    Metastatic symptoms

    • Liver metastases, causing:
      • Jaundice
      • Pain in the abdomen, more often the upper part of epigastrium or right side of the abdomen
      • liver enlargement, usually felt by a doctor

      Risk factors

      The lifetime risk of developing colon cancer in the United States is about 7%. Certain factors increase a person's risk of developing the disease. These include:

      • Age. The risk of developing colorectal cancer increases with age. Most cases occur in the 60s and 70s, while cases before age 50 are uncommon unless a family history of early colon cancer is present.
      • Polyps of the colon, particularly adenomatous polyps, are a risk factor for colon cancer. The removal of colon polyps at the time of colonoscopy reduces the subsequent risk of colon cancer.
      • History of cancer. Individuals who have previously been diagnosed and treated for colon cancer are at risk for developing colon cancer in the future. Women who have had cancer of the ovary, uterus, or breast are at higher risk of developing colorectal cancer.
      • Heredity:
        • Family history of colon cancer, especially in a close relative before the age of 55 or multiple relatives
        • Familial adenomatous polyposis (FAP) carries a near 100% risk of developing colorectal cancer by the age of 40 if untreated
        • Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome

        Alcohol

        The WCRF panel report Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective finds the evidence "convincing" that alcoholic drinks increase the risk of colorectal cancer in men.

        
        

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