What does colorectal mean?
Colorectal is a word which means 'the colon and rectum'. The colon and rectum are parts of the gut (gastrointestinal tract). The gut starts at the mouth and ends at the anus. When we eat or drink the food and liquid travel down the oesophagus (gullet) into the stomach. The stomach churns up the food and then passes it into the small intestine.
The small intestine (sometimes called the small bowel) is several metres long and is where food is digested and absorbed. Undigested food, water and waste products are then passed into the large intestine (sometimes called the large bowel). The main part of the large intestine is called the colon which is about 150 cm long. This is split into four sections, the ascending, transverse, descending, and sigmoid colon. Some water and salts are absorbed into the body from the colon. The colon leads into the rectum (back passage) which is about 15 cm long. The rectum stores faeces (stools) before they are passed out from the anus.
What is cancer?
Cancer is a disease of the cells in the body. The body is made up from millions of tiny cells. There are many different types of cell in the body, and there are many different types of cancer which arise from different types of cell. What all types of cancer have in common is that the cancer cells are abnormal and multiply 'out of control'.
A malignant tumour is a 'lump' or 'growth' of tissue made up from cancer cells which continue to multiply. Malignant tumours invade into nearby tissues and organs which can cause damage.
Malignant tumours may also spread to other parts of the body. This happens if some cells break off from the first (primary) tumour and are carried in the bloodstream or lymph channels to other parts of the body. These small groups of cells may then multiply to form 'secondary' tumours (metastases) in one or more parts of the body. These secondary tumours may then grow, invade and damage nearby tissues, and spread again.
Some cancers are more serious than others, some are more easily treated than others (particularly if diagnosed at an early stage), some have a better outlook (prognosis) than others.
So, cancer is not just one condition. In each case it is important to know exactly what type of cancer has developed, how large it has become, and whether it has spread. This will enable you to get reliable information on treatment options and outlook.
See separate leaflet called 'What are Cancer and Tumours' for further details about cancer in general.
What is colorectal cancer?
Colorectal cancer is a cancer of the colon or rectum. It is sometimes called bowel cancer or cancer of the large intestine. It is one of the most common cancers in the UK. (In contrast, cancer of the small intestine is rare.) Colorectal cancer can affect any part of the colon or rectum, but most commonly first develops in the lower part of the descending colon, the sigmoid colon, or rectum.
In most cases, colorectal cancer develops from a polyp which has formed on the lining of the colon or rectum (see below). Sometimes colorectal cancer begins from a cell within the lining of the colon or rectum which becomes cancerous.
(Some rare types of cancer arise from various other cells in the wall of the colon or rectum. For example, carcinoid, lymphoma, and sarcomas. These are not dealt with further in this leaflet.)
As the cancer cells multiply they form a tumour. The tumour invades deeper into the wall of colon or rectum. Some cells may break off into the lymph channels or bloodstream. The cancer may then spread (metastasise) to lymph nodes nearby or to other areas of the body, most commonly the liver and lungs.醫(yī).學(xué) 全在.線提供www.med126.com
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 (non-cancerous) 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?
A cancerous tumour starts from one abnormal cell. In the case of colorectal cancer, it is a cell in a polyp which is the most common site for a cancerous cell to develop. 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 '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. These include:
Protective factors
There is a reduced risk of developing colorectal cancer in:
