Colorectal cancer
commonly known as bowel cancer, is a cancer caused by uncontrolled cell growth (neoplasia), in the colon, rectum, or vermiform appendix colorectal cancer is clinically distinct from anal cancer, which affects the anus.
Colorectal cancers start in the lining of the bowel. If left untreated, it can grow into the muscle layers underneath, and then through the bowel wall. Most begin as a small growth on the bowel wall: a colorectal polyp or adenoma. These mushroom-shaped growths are usually benign, but some develop into cancer over time. Localized bowel cancer is usually diagnosed through colonoscopy.
Invasive cancers that are confined within the wall of the colon (TNM stages I and II) are often curable with surgery, For example, in England over 90% of patients diagnosed at this stage will survive the disease beyond 5 years. However, if left untreated, the cancer can spread to regional lymph nodes (stage III). In England, around 48% of patients diagnosed at this stage survive the disease beyond five years.Cancer that has spread widely around the body (stage IV) is usually not curable; approximately 7% of patients in England diagnosed at this stage survive beyond five years.
Colorectal cancer is the third most commonly diagnosed cancer in the world, but it is more common in developed countries. Around 60% of cases were diagnosed in the developed world. GLOBOCAN estimated that, in 2008, 1.24 million new cases of colorectal cancer were clinically diagnosed, and that this type of cancer killed 610,000 people.
Signs and symptoms
The symptoms of colorectal cancer depend on the location of tumor in the bowel, and whether it has spread elsewhere in the body (metastasis). While no symptom is diagnostic of colorectal cancer, rectal bleeding or anemia are high risk features.
Local symptoms are more likely if the tumor is located closer to the anus. There may be a change in bowel habit (such as unusual and unexplained constipation or diarrhea), and a feeling of incomplete defecation (rectal tenesmus). Lower gastrointestinal bleeding, including the passage of bright red blood in the stool, may indicate colorectal cancer, as may the increased presence of mucus. Melena, black stool with a tarry appearance, normally occurs in upper gastrointestinal bleeding (such as from a duodenal ulcer), but is sometimes encountered in colorectal cancer when the disease is located in the beginning of the large bowel.
A tumor that is large enough to fill the entire lumen of the bowel may cause bowel obstruction. This situation is characterized by constipation,abdominal pain, abdominal distension and vomiting. This occasionally leads to the obstructed and distended bowel perforating and causingperitonitis. A large left colonic tumor may compress the left ureter and cause hydronephrosis.
Certain local effects of colorectal cancer occur when the disease has become more advanced. A large tumor is more likely to be noticed on feeling the abdomen, and it may be noticed by a doctor on physical examination. The disease may invade other organs, and may causeblood or air in the urine (invasion of the bladder) or vaginal discharge (invasion of the female reproductive tract).
If a tumor has caused chronic bleeding in the bowel, iron deficiency anemia may occur, causing a range of symptoms that may includefatigue, palpitations and pale skin (pallor). Colorectal cancer may also lead to weight loss, generally due to a decreased appetite
There may be rarer symptoms including unexplained fever or thrombosis, usually deep vein thrombosis. Such symptoms, known asparaneoplastic syndrome, are due to the body's immune response to the cancer, rather than the tumor itself.
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