结肠镜检查 - 乙状结肠癌

                               
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Colorectal cancer (also called cancer of the bowel or bowel cancer). Most cases occur in people aged over 50. If colorectal cancer is diagnosed at an early stage, there is a good chance of a cure. In general, the more advanced the cancer (the more it has grown and spread), the less chance that treatment will be curative. However, treatment can often slow the progress of the cancer.
Polyps and colorectal cancer
A bowel polyp (adenoma) is a small growth that sometimes forms on the inside lining of the colon or rectum. Most bowel polyps develop in older people. About 1 in 4 people over the age of 50 develop at least one bowel polyp. Polyps are benign (noncancerous) and usually cause no problems.

However, sometimes a benign polyp can turn cancerous. If one does turn cancerous, the change usually takes place after a number of years. Most colorectal cancers develop from a polyp that has been present for 5-15 years.

What causes colorectal cancer?
The exact reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply out of control.

See separate leaflet called 'Cancer - What Causes Cancer?' for more details.

Risk factors
Although colorectal cancer can develop for no apparent reason, there are certain risk factors which increase the chance that colorectal cancer will develop. Risk factors include:

Ageing. Colorectal cancer is more common in older people. Eight out of ten people who are diagnosed with colorectal cancer are older than 60 years.
If a close relative has had colorectal cancer (there is some genetic factor).
If you have familial adenomatous polyposis or hereditary non-polyposis colorectal cancer. However, these are rare inherited disorders.
If you have ulcerative colitis or Crohn's disease (conditions of the colon) for more than 8-10 years.
Obesity.
Lifestyle factors: little exercise, drinking a lot of alcohol.