What is Cancer
Cancer Type

Bowel cancer (colorectal)

The digestive system
The bowel is part of the digestive system, which is sometimes called the gastrointestinal (GI) or digestive tract. The digestive system starts at the mouth and ends at the anus. It helps the body to break down food and turn it into energy. It also gets rid of parts of food that the body doesn't use. This solid waste matter is called stools or faeces.
Parts of the bowel
There are two main parts of the bowel:
  • Small bowel: a 4m to 6m long tube that takes food from the stomach and absorbs nutrients. Also called the small intestine.
  • Large bowel: absorbs water and salts and turns what is left over into waste (stools or faeces). Also called the large intestine.
The large bowel has several sections. 

Parts of the large bowel:-
Caecum A pouch at the beginning of the large bowel 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. The colon is divided into four parts (ascending colon, transverse colon, descending colon and sigmoid colon) and stretches from the caecum to the rectum. It is about 1.5m long.
Rectum The last 15cm to 20cm of the large bowel.
Anus The opening at the end of the digestive tract. The anus has strong muscles that keep it closed. During a bowel motion, these muscles relax to release stools 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's sometimes also known as colorectal cancer.
Bowel cancer grows from the inner lining of the bowel (mucosa). It may develop from growths on the bowel wall called polyps. Polyps are usually harmless (benign), but they may become cancerous (malignant) over time. Malignant polyps may be small or large, flat or mushroom-shaped.
If untreated, bowel cancer can grow locally 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, it develops fairly slowly and stays in the bowel for months or years before spreading.
How common is it ?
According to the Globocan (2012), bowel cancer ranks as the second most common cancer in males and the third most common cancer in females in Malaysia. For Malaysian men, it comprises 14.1% of all new cancers, with an increased incidence for men in the age group of 50 and above, but can occur at any age.
In its early stages, bowel cancer often has no symptoms. However, some people may experience the following:
  • a change in bowel habits, 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 who has these symptoms has bowel cancer. Other medical conditions, such as haemorrhoids or tears in anal tissue, and some food or medications, can also cause these changes. If you have any of the above symptoms for more than two weeks, see your doctor for a check-up.
What are the risk factors?
The exact cause of bowel cancer isn't known. However, some factors increase the chance of developing it:
  • getting older: bowel cancer most commonly affects people over the age of 50
  • 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 8 to 10 years
  • lifestyle factors: being overweight, doing little physical activity, a diet high in fat or animal products, high alcohol consumption and smoking can play a part
  • other diseases: people who have had colorectal cancer are more likely to develop another bowel cancer; some people who've had ovary, endometrium or breast cancer may also be more likely to develop it
  • Ashkenazi Jewish heritage: people from this background are more likely to develop bowel cancer
  • inheriting a rare genetic disorder: see below for more information about familial adenomatous polyposis and Lynch syndrome
  • strong family history; linked to inherited genetic conditions
Polyps in the bowel are a risk factor for bowel cancer. If polyps are removed, the risk of bowel cancer is reduced but it can still occur.
Inherited genetic conditions
There are two rare conditions running in families that cause a small number (5% to 6%) of bowel cancers:
  1. Familial adenomatous polyposis (FAP): This condition causes many polyps to form in the bowel. If polyps caused by FAP aren't removed, they become cancerous.
  2. Lynch syndrome: This increases the risk of developing bowel cancer and other cancers. It was previously known as hereditary non-polyposis colorectal cancer (HNPCC).
Family history of cancer
If one or more of your family members (such as a parent, sibling or grandparent) have been diagnosed with bowel cancer, it may run in your family. This is a possibility if two relatives on the same side of your family have cancer, or if they were diagnosed before the age of 55.

Other cancers, such as breast cancer, can also run in the family, and this may increase your risk of developing bowel cancer. If you're concerned about your family history, see your general practitioner (GP) for regular check-ups and discuss whether you should have a further assessment.
Doing regular physical activity, maintaining a healthy weight and eating a diet high in fruit, vegetables and fibre may help protect against bowel cancer. 
Reviewed By:
Karen Barclay, Colorectal Surgeon, The Northern Hospital, Lecturer in Surgery, University of Melbourne, VIC; Carole Arbuckle, Cancer Nurse, Cancer Council VIC; Karen Bowers, Eat it to Beat it Strategy Project Officer, Cancer Council NSW; Darrell Bowyer, Consumer; Rebecca Foot-Connolly, Stomal Therapy Nurse, The Alfred Hospital, VIC; Bernadette Hadfield, Stomal Therapy Nurse, The Alfred Hospital, VIC; Melissa Heagney, Media and Communications Advisor, Cancer Prevention Unit, Cancer Council VIC; Dorothy King, Consumer; and Loreto Pinnuck, Stomal Therapist, Wound Consultant, Paediatric Continence Specialist, Monash Medical Centre, VIC. Thanks to Paul Zuiderwyk for sharing his story.