Bowel (Colorectal) Cancer - symptoms, treatment, prevention

 

Bowel cancer is a cancer that affects the digestive system between the stomach and the anus. It can affect either the small bowel where our food is digested, or the large bowel (colon and rectum) where what remains of our food is turned into solid waste and expelled from the body. This page deals primarily with cancer of the large bowel (also known as colon or colorectal cancer) which is more common than small bowel cancer.

Characteristic symptoms of colorectal cancer include changes in bowel habits and bleeding from the bottom. Treatment will involve surgery, followed in some cases by chemotherapy or radiation therapy. In many cases colorectal cancer is curable if detected sufficiently early in the course of the disease.

Signs, symptoms, and diagnosis

Signs and symptoms of colorectal cancer are many and varied, including:

• Blood in the stools and/or bleeding from the rectum
• A change in bowel habit lasting longer than 6 weeks (e.g. loose stools, diarrhoea or constipation)
• Stomach pain (often severe)
• Lumps or a mass in the abdomen
• Weight loss
• Weakness and tiredness (symptoms of anaemia).

A diagnosis of colorectal cancer is made by a combination of tests including a digital rectal examination (where your doctor will feel for suspicious lumps using a gloved finger), testing for blood in the stools (faecal occult blood test), and x-rays of the digestive tract.

The definitive test for colorectal cancer is a colonoscopy. A colonoscopy is performed by a colorectal surgeon or gastroenterologist using a colonoscope (a thin, flexible, tubular instrument with a video camera at one end) to view the lining of the intestines and, if necessary, to take biopsy tissue samples for laboratory testing.

Causes

It is not known what causes bowel / colorectal cancer, but several risk factors that appear to increase the likelihood of developing the disease have been identified. 

A family history of bowel cancer or polyps – having a first-degree relative (father, mother, brother, sister) or second-degree (grandfather, grandmother, aunt, uncle) relative with bowel cancer or polyps – is a risk factor for bowel cancer. 

The risk of developing the condition is also increased in people with an inflammatory bowel disease, primarily long term ulcerative colitis but also some instances of Crohn's disease. 

Diets high in fat are believed to be a factor in the development of bowel cancer – countries with high rates of bowel cancer have a higher consumption of fat than countries with low bowel cancer rates. It is thought that digestion of fat in the colon results in the formation of cancer-causing chemicals (carcinogens). Consuming less fat should help to reduce exposure to these fat-derived carcinogens.

Staging of colorectal cancer

When colorectal cancer is diagnosed, additional tests are performed to determine the extent of the disease, which is a process called staging. The staging for colorectal cancer is as follows:

• Stage I (least advanced cancer) – cancer involving only the innermost layers of the colon or rectum wall. The likelihood of cure for stage I cancer is over 90%, emphasizing the importance of early detection of the cancer
• Stage II – cancer exhibiting greater growth and extension of tumour through the wall of the colon or rectum into adjacent structures.
• Stage III – cancer involving spread of the cancer to local lymph nodes (metastasis).
• Stage IV (most advanced cancer) – cancer having spread to distant organs, usually the liver and lungs, or lymph nodes far from the original tumour. 

• Prevention

  The specific cause of bowel cancers is not known but lifestyle factors may contribute to its development. Therefore, making the following lifestyle changes, or modifications, may lower the risk of bowel cancers:
  • Maintaining a healthy body weight
  • Being physically active
  • Eating a diet rich in whole grains, cereals, fruit and vegetables
  • Reducing intake of fats, salt and sugars
  • Drinking alcohol in moderation
  • Stopping smoking.

Treatment

The primary treatments for colorectal cancer are surgery to remove cancer cells, and chemotherapy and radiation therapy to kill cancer cells. 

For most people with stage I and stage II colorectal cancer, surgery alone is the only treatment required. However, once the cancer has spread to local lymph nodes (stage III), the risk of the cancer returning remains high even if all visible evidence of the cancer has been removed by the surgery. In this case, chemotherapy is likely to be used to lower the risk of the cancer returning. 

There are several different options for chemotherapy for the treatment of colorectal cancer. The simplest treatments involve a single type of chemotherapy drug, given either by pill or by injection into a vein, but sometimes a combination of chemotherapy drugs is recommended. Chemotherapy is typically given for a total of 6 months. 

Once colorectal cancer has spread to other parts of the body (stage III and IV cancer), chemotherapy is the best treatment, and although not curative it can extend life expectancy and quality of life. 

Radiation therapy is usually used for cancer of the rectum, since tumours in the rectum are often more difficult to remove surgically than are tumours in other parts of the bowels.