For GPs

Colorectal Cancer

Every year over 14,000 people in Australia develop colorectal cancer (also called bowel cancer). Bowel cancer occurs when abnormal cells in the bowel multiply faster than normal, causing a swelling or tumour. These cancerous cells can grow into the surrounding bowel wall and also travel to other sites, such as the liver, brain, lungs and lymph nodes. These secondary tumours are called metastases.

There are several names for bowel cancer, including colon cancer, rectal cancer and anal cancer, all named for the different parts. Because the bowel is such a long organ, tumours arising at different sites can cause different problems depending on if they occur at the start, middle, or end of the colon. They also require and respond to different treatments.

Bowel cancer can grow without any symptoms until the cancer is quite large, or has spread outside to the liver or another site. If bowel cancer spreads outside the bowel it is treatable, however ‘cure’ is not always  possible.

    • What are the Causes of Bowel Cancer?

      The exact cause is not known, however just getting older increases your risk of developing bowel cancer. There are lifestyle factors such as cigarette smoking, high fat and low fibre diet and a lack of exercise that are thought to increase the incidence of bowel cancer.

      Certain genetic conditions and a strong history of bowel cancer in the family also increase the risk. Some kinds of bowel polyps are a risk factor for developing bowel cancer, however if the polyp is removed, the risk is dramatically reduced.

    • What are the Symptoms of Bowel Cancer?

      Common bowel cancer symptoms include change in bowel habit (constipation, diarrhoea, smaller stools), blood in the stools, weight loss, pain and anaemia.
      Ideally bowel cancer is detected when the cancer is small and limited to the bowel.
      Small amounts of blood seen on faecal testing but not visible to the naked eye, is often how early bowel cancers are detected in screening programs of healthy people.
      Bowel cancer symptoms depend a lot on the site and size of the tumour in the bowel.

      Symptoms of advanced bowel cancer may include:

      • pain in the abdomen or pelvis, or
      • can be caused by secondary deposits, or metastases, if bowel cancer travels to other organs:
      • abdominal pain (liver),
      • cough, shortness of breath (lung),
      • pain (bones), or
      • headache or fitting (brain).
    • What are the Treatments for Bowel Cancer?

      The available treatments for bowel cancer depend on the stage at which the cancer has been diagnosed, as well as the general health of the individual. If the cancer is diagnosed very early then surgery may be all that is required.  However, often surgery is followed by chemotherapy (drug treatment) or radiation therapy depending on the site of the cancer.

      Radiation therapy is used very commonly for rectal (lower bowel) cancers.  Combined chemotherapy and radiation therapy is often used for cancers in the rectum before surgery is performed to improve the chance of the tumour being completely removed by the surgeon.

      Sometimes radiation therapy is given after surgery if it looks like the cancer has not all been removed or if lymph nodes (glands) are found to have cancer in them. Radiation therapy alone can also be used if surgery is not possible. Combined chemotherapy and radiation therapy without any surgery is usually the best treatment for certain anal cancers and allows the anal function to be maintained.

    • What are the Side Effects of Radiation Therapy?

       Side effects during / soon after treatment (Early or “acute” side effects) General

      • Fatigue
      • Nausea (Uncommon)


      • Rectal discomfort
      • Bowel urgency and frequency
      • Bladder urgency and frequency

      What can help reduce acute side effects?

      There are many ways to minimise the side effects during treatment. It is important that you let the treating team know about any side effects you are experiencing. Your doctors may advise supportive measures or prescribe medications to relieve some of these symptoms. The team is here to support you throughout your treatment.

      Side effects well after treatment (Late or long-term side effects)

      Most people tolerate treatment well for many years after treatment. There are some rare side effects that can happen in the long-term. You should speak to your doctor if these rare side effects occur.

      • Small bowel – bleeding, stricture, perforation, malabsorption (Very uncommon)
      • Rectal damage – reduced capacity, urgency, frequency, bleeding, incontinence, fistula formation (Very uncommon)

      What can be done to treat late side effects?

      You should speak to your doctor if these rare side effects occur. Depending on the side effect, your doctor may refer you to a specialist or surgeon to manage these.

How Do I Enquire About Radiation Therapy with My Healthcare Professional?

The best person to discuss radiation therapy with for bowel cancer is a Radiation Oncologist. You can ask your Surgeon or General Practitioner for a referral to a Radiation Oncologist for a discussion about whether radiation therapy is a suitable treatment for you.

Visit ‘For GPs and other Health Professionals’ and ‘Talking to your doctor’ sections for further information.

Find your closest radiation oncology Treatment Centre

Page last updated: 24/04/2019