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Bowel cancer, also called colorectal cancer, begins when cells that line the colon or rectum in the bowel (large intestine) change and begin to grow out of control, forming a tumour. Bowel cancer is considered one of the most treatable cancers if detected early. However, it is sometimes not detected until at an advanced stage. In Australia, it is responsible for the second highest number of cancer deaths after lung cancer.
Although younger people can be affected, the majority of bowel cancer cases occur in people older than 50 years. In Australia, the risk of developing bowel cancer before the age of 85 is about 1 in 12. The five-year survival rate for this type of cancer is approximately 66%.
The most common type of bowel cancer is called an adenocarcinoma, which is a cancer of the cells that line the colon or rectum. Other rarer types include squamous cell cancers (which start in the skin-like cells of the bowel lining), carcinoid tumours, gastrointestinal stromal tumours, sarcomas and lymphomas.
In most cases, bowel cancer is thought to develop from growths in the colon called adenomas, or polyps. Not all polyps become cancerous, but if they do, cancer can spread through some or all of the tissue layers making up the colon and rectum, often over a period of several years.
Aside from the presence of polyps (especially large polyps, or a large number of them), there are a number of other factors thought to increase a person’s risk of developing bowel cancer. These include:
• a family history of bowel cancer or polyps
• type 2 diabetes
• inflammatory bowel disease
• ovarian cancer or uterine cancer (in women)
• certain inherited genetic conditions, e.g. familial adenomatous polyposis (FAP), hereditary non-polyposis colon cancer (HNPCC), Turcot syndrome.
In addition, several lifestyle related factors have been linked to bowel cancer, including:
• a diet high in red meats and processed meats
• physical inactivity
• long-term smoking
• heavy alcohol use
In most cases where DNA mutations lead to bowel cancer, these mutations are not inherited. It is not yet understood what causes them, although in many cases there appears to be involvement of a gene called the APC gene. Other genes are also be involved in causing cells to grow and spread uncontrollably, and research is continuing to try to understand these factors.
Bowel cancer is usually slow-growing and often shows no symptoms in the early stages. The most common symptoms are:
• bleeding from the rectum (this may be noticed as blood in the stool)
• a change in bowel habit (loose stools or constipation)
• anaemia (low red blood cells, leading to paleness, fatigue etc)
• unexplained weight loss
• abdominal pain or cramping
• unexplained tiredness or fatigue.
Bowel cancer is diagnosed using a number of tests, including:
• blood tests
• internal examination of the rectum, anus and colon (colonoscopy/sigmoidoscopy).
Imaging tests such as ultrasound, x-rays, MRI or CT scans may also be used to help with diagnosis and to learn how far the cancer may have spread.
Treatment depends on the size of the tumour, how deeply the cancer has penetrated the layers of the colon or rectum, and whether it has spread to other organs such as the liver.
If the cancer is restricted to a small area and has not yet spread, surgery to remove the cancer and surrounding tissue (including nearby lymph nodes) may be all that is required. In other cases, chemotherapy and/or monoclonal antibodies may be given. Chemotherapy may be given either before surgery (to shrink the tumour), or after surgery (to kill any cancer cells remaining in the body).
Currently in Australia, targeted therapies are being trialled as a treatment for bowel cancer. Research into new treatment drugs is ongoing, including a drug called called everolimus, which preliminary studies have indicated may help reduce tumour size as well as the development of new tumours.
International research teams are also working on developing a vaccine for bowel cancer, designed to boost the body’s immune reaction to bowel cancer.
After treatment for bowel cancer, regular follow-up examinations and/or medical tests need to be done to look for any signs of the cancer returning, as well as to check for any late effects caused by treatment.
During and after recovery, healthy lifestyle practices are encouraged, such as maintaining a healthy weight, being physically active, not smoking, and eating well.