Bowel cancer

Sunday 1 February, 2015

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 On this page: What is bowel cancer? | How common is it? | What are the symptoms? | What are the risk factors? | Can bowel cancer run in families?

The bowel

The bowel is part of the digestive system, which is also called the gastrointestinal (GI) or digestive tract. The digestive system starts at the mouth and ends at the anus. It helps the body break down food and turn it into energy. It also gets rid of the parts of food the body does not use. This solid waste matter is called faeces (also known as stools when it leaves the body through the anus). The bowel is made up of the small bowel and the large bowel.

Small bowel
A long tube (4–6 m) that absorbs nutrients from food. Also called the small intestine, it is longer but narrower than the large bowel. 

Duodenum The first section of the small bowel; receives food from the stomach.
Jejunum The middle section of the small bowel.
Ileum The final and longest section of the small bowel; transfers waste to the large bowel.

Large bowel
A tube that absorbs water and salts and turns what is left over into waste (faeces). Also called the large intestine, the large bowel is about 1.5 m long.

Caecum A pouch that receives waste from the small bowel. The appendix is a small tube hanging off the end of the caecum.
Colon The main working area of the large bowel. Takes up most of the large bowel’s length and has four parts: ascending colon, transverse colon, descending colon and sigmoid colon.
Rectum The last 15–20 cm of the large bowel.
Anus The opening at the end of the digestive tract. During a bowel motion, the muscles of the anus relax to release faeces from the rectum.


The digestive system

What is bowel cancer?

Bowel cancer is cancer in any part of the large bowel (colon or rectum). It is sometimes known as colorectal cancer and might also be called colon cancer or rectal cancer, depending on where it starts. Cancer of the small bowel is very rare and is usually called ‘small bowel cancer’ or ‘small intestine cancer’.

Bowel cancer grows from the inner lining of the bowel (mucosa). It usually develops from growths on the bowel wall called polyps. Most polyps are harmless (benign), but some become cancerous (malignant) over time.

If untreated, bowel cancer can grow into the deeper layers of the bowel wall. It can spread from there to the lymph nodes (glands). These small, bean-shaped masses are part of the body’s lymphatic system. If the cancer advances further, it can spread to other organs, such as the liver or lungs (metastasis).

In most cases, the cancer develops slowly and stays in the bowel for months or years before spreading.

How common is it?

Bowel cancer is the second most common cancer affecting people in Australia. It is estimated that about 17,000 people are diagnosed with bowel cancer every year. About one in 19 men and one in 28 women will develop bowel cancer before the age of 75. It is most common in people over 50, but it can occur at any age.

What are the symptoms?

In its early stages, bowel cancer often has no symptoms. However, some people with bowel cancer do experience persistent symptoms. These can include:

  • a change in bowel habit, such as diarrhoea, constipation or smaller, more frequent bowel movements
  • a change in appearance of bowel movements (e.g. narrower stools or mucus in stools)
  • a feeling of fullness or bloating in the bowel or rectum
  • a feeling that the bowel hasn’t emptied completely after a bowel movement
  • blood in the stools or on the toilet paper
  • unexplained weight loss
  • weakness or fatigue
  • rectal or anal pain
  • a lump in the rectum or anus
  • abdominal pain or swelling
  • a low red blood cell count (anaemia), which can cause tiredness and weakness.

Not everyone with these symptoms has bowel cancer. Other conditions, such as haemorrhoids, diverticulitis (inflammation of pouches in the bowel wall), or tears in the anal canal, and some foods or medications, can also cause these changes.

Short-term changes in bowel function are very common and usually do not indicate a serious problem. However, if you have any of the above symptoms for more than four weeks, see your doctor for a check-up.

What are the risk factors?

The exact cause of bowel cancer is not known. However, some factors increase the chance of developing it.

Risk factors include:

  • age – bowel cancer most commonly affects people over the age of 50
  • polyps – having a large number of polyps in the bowel
  • bowel diseases – people who have an inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis, have a significantly increased risk, particularly if they have had it for more than eight years
  • lifestyle factors – being overweight, having a diet high in red meat (particularly processed meats such as salami or ham), drinking alcohol and smoking increase the risk
  • other diseases – people who have had bowel cancer once are more likely to develop a second bowel cancer; some people who have had ovarian or endometrial cancer may have an increased risk of bowel cancer
  • strong family history – see below
  • rare genetic disorders – see below.

Being physically active, maintaining a healthy weight and eating a high-fibre diet may help protect against bowel cancer. 

Although the average age at which bowel cancer is diagnosed is 69 years, about 7% of bowel cancers are in people younger than 50. 

Can bowel cancer run in families?

Sometimes bowel cancer runs in families. If one or more of your close family members (such as a parent or sibling) have had bowel cancer, it may increase your risk. This is especially the case if they were diagnosed before the age of 55, or if there are two close relatives on the same side of your family with bowel cancer.

A family history of other cancers, such as endometrial cancer, may also increase your risk of developing bowel cancer.

There are also two rare genetic conditions that occur in some families. These cause a small number (5–6%) of bowel cancers.

  • Familial adenomatous polyposis (FAP): This condition causes hundreds of polyps to form in the bowel. If polyps caused by FAP are not removed, they will become cancerous.
  • Lynch syndrome: Previously known as hereditary non‑polyposis colorectal cancer (HNPCC), this syndrome is characterised by a fault in the gene that helps DNA repair itself. Having Lynch syndrome increases the risk of developing bowel cancer and other cancers.
If you are concerned about your family risk factors, talk to your doctor about having regular check-ups or ask for a referral to a family cancer clinic. To find out more, call Cancer Council 13 11 20. 
Reviewed by: Mr Chip Farmer, Colorectal Surgeon, The Alfred Hospital, Cabrini Hospital and The Avenue Hospital, VIC; Mervyn Bartlett, Consumer; Dr Andrew Haydon, Medical Oncologist, The Alfred Hospital and Cabrini Hospital, VIC; Jackie Johnston, Palliative Care and Stomal Therapy Clinical Nurse Consultant, St Vincent’s Private Hospital (Darlinghurst), NSW; Dr Shahrir Kabir, Fellow in Colorectal Surgery, Royal Brisbane and Women’s Hospital, QLD; Steve Pratt, Nutrition and Physical Activity Manager, Cancer Council WA; Cassie Riley, Cancer Nurse Coordinator – Colorectal, WA Cancer and Palliative Care Network, WA; Mary Shanahan, Cancer Genetics Nurse Coordinator, Peter MacCallum Cancer Centre, VIC; A/Prof Andrew Stevenson, Head of Colorectal Surgery, Royal Brisbane and Women’s Hospital, University of Queensland; Pat Walls, Clinical Nurse Consultant Stomal Therapy/Wound Management, Holy Spirit Northside Private Hospital, QLD. 
Updated: 01 Feb, 2015