Colorectal CancerColorectal cancer is cancer that starts in either the colon or the rectum. Colon cancer and rectal cancer have many features in common. They are discussed together here except for the section about treatment, where they are discussed separately.
The normal digestive systemColon and rectal cancers begin in the digestive system, also called the GI (gastrointestinal) system (see the picture below). This is where food is processed to create energy and rid the body of solid waste matter (stool). In order to understand colorectal cancer, it helps to know something about the structure of the digestive system and how it works.
After food is chewed and swallowed, it travels to the stomach. There it is partly broken down and sent to the small intestine. The word "small" refers to the width of the small intestine. In fact, the small intestine is the longest part of the digestive system -- about 20 feet.
The small intestine also breaks down the food and absorbs most of the nutrients. The small intestine leads to the large intestine (also called the large bowel or colon), a muscular tube about 5 feet long. The colon absorbs water and nutrients from the food and also serves as a storage place for waste matter. The waste matter (stool) moves from the colon into the rectum, the last 6 inches of the digestive system. From there the waste passes out of the body through the opening called the anus.
The wall of the colon and rectum has several layers of tissues. Colorectal cancer starts in the inner layer and can grow through some or all of the other layers. The stage (extent of spread) of a cancer depends to a great degree on how deep the cancer goes into these layers.
Abnormal growths in the colon or rectumCancer that starts in these different areas may cause different symptoms. But colon cancer and rectal cancer have many things in common. In most cases, colorectal cancers develop slowly over many years. We now know that most of these cancers begin as a polyp--a growth of tissue that starts in the lining and grows into the center of the colon or rectum. This tissue may or may not be cancer. A type of polyp known as an adenoma can become cancer. Removing a polyp early may keep it from becoming cancer.
The colon is the part of the digestive system where the waste material is stored. The rectum is the end of the colon adjacent to the anus. Together, they form a long, muscular tube called the large intestine (also known as the large bowel). Tumors of the colon and rectum are growths arising from the inner wall of the large intestine. Benign tumors of the large intestine are called polyps. Malignant tumors of the large intestine are called cancers. Benign polyps do not invade nearby tissue or spread to other parts of the body. Benign polyps can be easily removed during colonoscopy and are not life-threatening.
If benign polyps are not removed from the large intestine, they can become malignant (cancerous) over time. Most of the cancers of the large intestine are believed to have developed from polyps. Cancer of the colon and rectum (also referred to as colorectal cancer) can invade and damage adjacent tissues and organs. Cancer cells can also break away and spread to other parts of the body (such as liver and lung) where new tumors form. The spread of colon cancer to distant organs is called metastasis of the colon cancer. Once metastasis has occurred in colorectal cancer, a complete cure of the cancer is unlikely.
Globally, cancer of the colon and rectum is the third leading cause of cancer in males and the fourth leading cause of cancer in females. The frequency of colorectal cancer varies around the world. It is common in the Western world and is rare in Asia and Africa. In countries where the people have adopted western diets, the incidence of colorectal cancer is increasing
Signs and SymptomsAlthough the exact cause of colon cancer is unknown, certain risk factors have been identified that may increase your chance of developing the disease.
These include: -
- Age — The majority of colon cancers are diagnosed in people aged 50 or older, although the disease affects all ages.
- Bowel disease — A history of colorectal cancer, intestinal polyps and diseases such as chronic ulcerative colitis and Crohn's disease increase your chance of developing colon cancer.
- Diet and exercise — A diet high in fat, particularly from animal sources, and an inactive, sedentary lifestyle can increase your chance of developing colon cancer.
- Ethnic background and race — Jews of Eastern European descent called, Ashkenazi Jews, have a higher rate of colon cancer. African-Americans and Hispanics have a higher death rate from colon cancer, which may be caused by insufficient screenings, poor diet and lack of exercise.
- Family history/genetic factors — Specific genes have been identified that increase your chance of having colon cancer. If you have a strong family history of colorectal cancer, as defined by cancer or polyps in a first-degree relative younger than 60 or two first-degree relatives of any age, you're at increased risk for developing colon cancer.
- Smoking and alcohol — Research suggests that smokers and heavy drinkers have an increased risk of developing colon cancer.
Common signs and symptoms of colon cancer include: -
- A change in bowel habits
- Diarrhea, constipation or feeling that the bowel does not empty completely
- Blood, either bright red or very dark in the stool
- Stools that are narrower than usual
- General abdominal discomfort such as frequent gas pains, bloating, fullness or cramps
- Weight loss with no known reason
- Constant tiredness
Does colon cancer run in families?
A. There are two inherited conditions which carry a substantially higher risk of colon cancer. In Familial Adenomatous Polyposis, affected family members develop thousands of small benign growths, called polyps, in the large intestine. Before the age of 40, one or more of these polyps will develop into a bowel cancer. In Hereditary Non-Polyposis Colorectal Cancer (also called Lynch Syndrome), patients develop cancer of the bowels and other organs, usually at an early stage. However, these conditions are very rare and only cause one in twenty cases of bowel cancer. Overall, the risk of bowel cancer doubles if you have a close relative (parent, bother or sister) with this cancer.
How is colon cancer treated?
A. Surgery is the main method of treatment. The part of the colon containing the tumour is chopped out and usually a colostomy is performed. In a colostomy, the end of the bowel is diverted to the surface of the abdomen, where the faeces are collected in a plastic bag. Sometimes this is a temporary measure and when the part of the colon that had the cancer has recovered, it can be reconnected to the rest of the bowel. However, if the tumour is in the lower rectum, then both the rectum and anus have to be removed and the colostomy will be permanent. Often patients are given radiotherapy or chemotherapy after the operation as this can kill off any remaining cancer cells.
Q. What are the side effects of treatment?
Surgery, of any sort, causes tiredness and some pain, but these pass. The long-term side effects of a colostomy are described above. The main side effects of chemotherapy can be thinning or loss of hair (which only happens with some drugs and is temporary), tiredness, diarrhoea, nausea, sore mouth and minor infections. These all stop when the treatment stops. Radiotherapy has some similar side effects (tiredness, diarrhoea and nausea) and some different ones: red and sore skin where the treatment was given and bladder inflammation, causing frequent and uncomfortable urination.
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