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Colon Cancer

Colon Cancer (Colorectal Cancer):

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 fourth most common form of cancer in the United States and the third leading cause of cancer-related death in the Western world.[1][2] Colorectal cancers arise from adenomatous polyps in the colon. These mushroom-shaped growths are usually benign, but some develop into cancer over time. Localized colon cancer is usually diagnosed through colonoscopy.

Invasive cancers that are confined within the wall of the colon (TNM stages I and II) are curable with surgery. If untreated, they spread to regional lymph nodes (stage III), where up to 73% are curable by surgery and chemotherapy. Cancer that metastasizes to distant sites (stage IV) is usually not curable, although chemotherapy can extend survival, and in rare cases, surgery and chemotherapy together have seen patients through to a cure.[3] Radiation is used with rectal cancer.

On the cellular and molecular level, colorectal cancer starts with a mutation to the Wnt signaling pathway. When Wnt binds to a receptor on the cell, that sets in motion a chain of molecular events that ends with β-catenin moving into the nucleus and activating a gene on DNA. In colorectal cancer, genes along this chain are damaged. Usually, a gene called APC, which is a “brake” on the Wnt pathway, is damaged. Without a working APC brake, the Wnt pathway is stuck in the “on” position.[3]

 

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). Most of the symptoms may occur in other diseases as well, and hence none of the symptoms mentioned here is diagnostic of colorectal cancer. Symptoms and signs are divided into local, constitutional (affecting the whole body) and metastatic (caused by spread to other organs).

Local

Local symptoms are more likely if the tumor is located closer to the anus. There may be a change in bowel habit (new-onset constipation or diarrhea in the absence of another cause), and a feeling of incomplete defecation (rectal tenesmus) and reduction in diameter of stool; tenesmus and change in stool shape are both characteristic of rectal cancer. 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 causing peritonitis. A large left colonic tumour 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 cause blood or air in the urine (invasion of the bladder) or vaginal discharge (invasion of the female reproductive tract).

Constitutional

If a tumor has caused chronic occult bleeding, iron deficiency anemia may occur; this may be experienced as fatigue, palpitations and noticed as pallor (pale appearance of the skin). Colorectal cancer may also lead to weight loss, generally due to a decreased appetite.

More unusual constitutional symptoms are an unexplained fever and one of several paraneoplastic syndromes. The most common paraneoplastic syndrome is thrombosis, usually deep vein thrombosis.

 

 

See also

References

  1. ^ “Cancer”. World Health Organization. February 2006. http://www.who.int/mediacentre/factsheets/fs297/en/. Retrieved 24 May 2007.
  2. ^ “Cancer”. National Cancer Institute. 2009. http://www.cancer.gov/cancertopics/commoncancers.
  3. ^ a b c d e f Markowitz SD, Bertagnolli MM (December 2009). “Molecular basis of colorectal cancer”. N. Engl. J. Med. 361 (25): 2449–60. doi:10.1056/NEJMra0804588. PMID 20018966.
  4. ^ Levin KE, Dozois RR (1991). “Epidemiology of large bowel cancer”. World J Surg 15 (5): 562–7. doi:10.1007/BF01789199. PMID 1949852.
  5. ^ Penn State University health and disease information
  6. ^ Strate LL, Syngal S (April 2005). “Hereditary colorectal cancer syndromes”. Cancer Causes Control 16 (3): 201–13. doi:10.1007/s10552-004-3488-4. PMID 15947872.
  7. ^ American Cancer Society Smoking Linked to Increased Colorectal Cancer Risk – New Study Links Smoking to Increased Colorectal Cancer Risk 6 December 2000
  8. ^ ‘Smoking Ups Colon Cancer Risk’ at Medline Plus
  9. ^ Chao A, Thun MJ, Connell CJ, et al. (January 2005). “Meat consumption

 

 

 

November 26, 2010 - Posted by | Cancers, Intestines, Stomach | , ,

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