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The bowel | How common is bowel cancer? | Symptoms | Risk factors | Genetic risk | Health professionals
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 in the bowel it starts.
Bowel cancer grows from the inner lining of the bowel (mucosa). It usually develops from small growths on the bowel wall called polyps. Most polyps are harmless (benign), but some polyps develop into cancer over time. Polyps can be removed during a colonoscopy to prevent them becoming cancerous.
If untreated, bowel cancer can grow into the deeper layers of the bowel wall. It can spread from there to the lymph nodes. If the cancer advances further, it can spread to other organs, such as the liver or lungs.
Cancer care pathways
For an overview of what to expect during all stages of your cancer care, from diagnosis to treatment and beyond, read or download the Guide to Best Cancer Care for bowel cancer. This resource is also available in Arabic, Chinese, Greek, Hindi, Italian, Tagalog and Vietnamese – see details on the site.
The bowel is part of the lower gastrointestinal tract, which is part of the digestive system. 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.
The small bowel (small intestine)
This is a long tube (4–6 m) that absorbs nutrients from food. It is longer but narrower than the large bowel. It has three parts:
- duodenum – the first section of the small bowel; receives broken-down food from the stomach
- jejunum – the middle section of the small bowel
- ileum – the final and longest section of the small bowel; transfers waste matter to the large bowel.
The large bowel (large intestine)
This tube is about 1.5 m long. It absorbs water and salts, and turns what is left over into solid waste matter (known as faeces, stools or poo when it leaves the body). The large bowel has three parts:
- 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, the colon 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.
This is the opening at the end of the bowel. During a bowel movement, the anal muscles relax to release faeces. Anal cancer is treated differently to bowel cancer, see Understanding Anal Cancer.
How common is bowel cancer?
Bowel cancer is the third most common cancer affecting people in Australia. It is estimated that about 15,500 people are diagnosed with bowel cancer every year. It is most common in people over 50, but it can occur at any age.
About 9 out of 10 bowel cancers are adenocarcinomas, which start in the glandular tissue lining the bowel. Rarely, other less common types of cancer can also affect the bowel. These include lymphomas, squamous cell carcinomas, neuroendocrine tumours and gastrointestinal stromal tumours. Cancer can also start in the small bowel (called small bowel cancer or small intestine cancer), but this is rare.
What are the symptoms?
In its early stages, bowel cancer may have no symptoms. This is why screening is important to increase the chance of an early diagnosis. However, many people with bowel cancer do experience symptoms. These can include:
- blood in faeces (poo) or on the toilet paper
- a change in bowel habit, such as diarrhoea, constipation or smaller, more frequent bowel movements
- a change in the look of faeces (e.g. narrower or with mucus)
- a feeling of fullness or bloating in the abdomen (belly) or a strange sensation in the rectum, often during a bowel movement
- a feeling that the bowel hasn’t emptied completely
- losing weight for no obvious reason
- 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 or iron deficiency), which can cause tiredness and weakness
- a blockage in the bowel.
Not everyone with these symptoms has bowel cancer. Other conditions, such as haemorrhoids, diverticulitis (inflammation of pouches in the bowel wall), inflammatory bowel disease or an anal fissure (cracks in the skin lining the anus), can also cause these changes. Changes in bowel function are common and often do not indicate a serious problem. However, any amount of bleeding is not normal, and you should see your doctor for a check-up.
What are the risk factors?
The exact cause of bowel cancer is not known. However, research shows that people with certain risk factors are more likely to develop bowel cancer. Risk factors include:
- older age – most people with bowel cancer are over 50, and the risk increases with age
- 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 or processed meats such as salami or ham, drinking alcohol and smoking
- strong family history – a small number of bowel cancers run in families (see below)
- 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 (uterine) cancer may have an increased risk of bowel cancer
- rare genetic disorders – a small number of bowel cancers are associated with an inherited gene (see below).
Some things reduce your risk of developing bowel cancer, including being physically active, maintaining a healthy weight, cutting out processed meat, cutting down on red meat, drinking less alcohol, not smoking, and eating wholegrains, dietary fibre and dairy foods. Talk to your doctor about whether you should take aspirin, which has been shown to reduce the risk of developing bowel cancer.
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 or more close relatives on the same side of your family with bowel cancer. A family history of other cancers, such as endometrial (uterine) cancer, may also increase your risk of developing bowel cancer.
Some people have an inherited faulty gene that increases their risk of developing bowel cancer. These faulty genes cause a small number (about 5–6%) of bowel cancers. There are two main genetic conditions that occur in some families:
- Familial adenomatous polyposis (FAP) – This condition causes hundreds of polyps to form in the bowel. If these polyps are not removed, they may become cancerous.
- Lynch syndrome – This syndrome is characterised by a fault in the gene that helps the cell's DNA repair itself.
If you are concerned about your family history, 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 on 13 11 20.
Which health professionals will I see?
Your general practitioner (GP) will arrange the first tests to assess your symptoms, or further tests if you have had a positive screening test. If these tests do not rule out cancer, you will usually be referred to a specialist, such as a colorectal surgeon or a gastroenterologist. The specialist will arrange further tests. If bowel cancer is diagnosed, the specialist will consider treatment options. Often these will be discussed with other health professionals at what is known as a multidisciplinary team (MDT) meeting. During and after treatment, you may see a range of health professionals who specialise in different aspects of your care.
|Health professionals you may see
||assists with treatment decisions; provides ongoing care in partnership with specialists
||diagnoses bowel cancer and performs bowel surgery
||diagnoses and treats disorders of the digestive system, including bowel cancer; may perform endoscopy
||treats cancer with drug therapies such as chemotherapy, targeted therapy and immunotherapy (systemic treatment)
||treats cancer by prescribing and overseeing a course of radiation therapy
|cancer care coordinator
||coordinates your care, liaises with MDT members, and supports you and your family throughout treatment; may be a clinical nurse consultant (CNC) or colorectal cancer nurse
||administers drugs and provides care, information and support throughout treatment
|stomal therapy nurse
||provides information about surgery and can support you to adjust to life with a temporary or permanent stoma
||recommends an eating plan to follow while you are in treatment and recovery
||provides advice for people with a strong family history of bowel cancer or with a genetic condition linked to bowel cancer
||links you to support services and helps you with emotional, practical or financial issues
|physiotherapist, exercise physiologist
||help restore movement and mobility, and improve fitness and wellbeing
||assists in adapting your living and working environment to help you resume usual activities after treatment
||help you manage your emotional response to diagnosis and treatment
|palliative care specialist* and nurses
||work closely with the GP and cancer specialists to help control symptoms and maintain quality of life
Asking your doctor questions will help you make an informed choice. You may want to include some of the questions below in your own list:
- What type of bowel cancer do I have?
- Has the cancer spread? If so, where has it spread? How fast is it growing?
- Are the latest tests and treatments for this cancer available in this hospital?
- Will a multidisciplinary team be involved in my care?
- Are there clinical guidelines for this type of cancer?
- What treatment do you recommend? What is the aim of the treatment?
- Are there other treatment choices for me? If not, why not?
- Will I need a stoma? If so, will it be temporary or permanent?
- Will you refer me to a stomal therapy nurse?
- If I don’t have the treatment, what should I expect?
- I’m thinking of getting a second opinion. Can you recommend anyone?
- How long will treatment take? Will I have to stay in hospital?
- Are there any out-of-pocket expenses not covered by Medicare or my private health cover? Can the cost be reduced if I can’t afford it?
- How will we know if the treatment is working?
- Are there any clinical trials or research studies I could join?
- What are the risks and possible side effects of each treatment?
- Will I have a lot of pain? What will be done about this?
- Can I work, drive and do my normal activities while having treatment?
- Will the treatment affect my sex life and fertility?
- Should I change my diet or physical activity during or after treatment?
- Are there any complementary therapies that might help me?
- How often will I need check-ups after treatment?
- If the cancer returns, how will I know? What treatments could I have?
Expert content reviewers:
A/Prof David A Clark, Colorectal Surgeon, Royal Brisbane and Women’s Hospital, and The University of Queensland, QLD, and The University of Sydney, NSW; A/Prof Siddhartha Baxi, Radiation Oncologist and Medical Director, GenesisCare Gold Coast, QLD; Dr Hooi Ee, Specialist Gastroenterologist and Head, Department of Gastroenterology, Sir Charles Gairdner Hospital, WA; Annie Harvey, Consumer; A/Prof Louise Nott, Medical Oncologist, Icon Cancer Centre, Hobart, TAS; Caley Schnaid, Accredited Practising Dietitian, GenesisCare, St Leonards and Frenchs Forest, NSW; Chris Sibthorpe, 13 11 20 Consultant, Cancer Council Queensland; Dr Alina Stoita, Gastroenterologist and Hepatologist, St Vincent’s Hospital Sydney, NSW; Catherine Trevaskis, Gastrointestinal Cancer Specialist Nurse, Canberra Hospital, ACT; Richard Vallance, Consumer.
Page last updated:
The information on this webpage was adapted from Understanding Bowel Cancer - A guide for people with cancer, their families and friends (January 2021). This webpage was last updated in March 2021.