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
• Bowel obstruction causing bowel pain, bloating and vomiting of stool-like material.
• A tumor in the abdomen, felt by patients or their doctors.
• Symptoms related to invasion by the cancer of the bladder causing hematuria (blood in the urine) or pneumaturia (air in the urine), or invasion of the vagina causing maloderous vaginal discharge. These are late events, indicative of a large tumor.

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
• Blood clots in the veins and arteries, a paraneoplastic syndrome related to hypercoagulability of the blood (the blood is "thickened")