Bowel Cancer (Colorectal Cancer)

Bowel cancer, also known as colorectal cancer, is one of the most common cancers diagnosed in Australia. Around 15,500 Australians are diagnosed each year, and it is the fourth most common cancer affecting both men and women. While it most frequently occurs in people over 50, it can develop at any age, and rates among younger adults are rising.

The good news is that bowel cancer is highly treatable when detected early. Many people with bowel cancer in its early stages have no symptoms at all, which is why screening and specialist assessment play such an important role. If you have concerns about your bowel health, or if you have been referred for further investigation, a gastroenterologist can assess your symptoms, arrange appropriate testing, and coordinate your care.

What is Bowel Cancer?

Bowel cancer develops in the large intestine, which is made up of the colon and the rectum. When the cancer originates in the colon, it may be referred to as colon cancer. When it begins in the rectum, the term rectal cancer is used. Together, these are described as colorectal cancer. The condition begins when abnormal cells in the lining of the bowel wall start to multiply in an uncontrolled way.

The colon itself is approximately 1.5 metres long and runs in four sections: the ascending colon on the right side of the abdomen, the transverse colon across the upper abdomen, the descending colon on the left, and the sigmoid colon, which connects to the rectum. The rectum is the final section of the large bowel, spanning approximately 15 centimetres before reaching the anus.

Cancer that begins in the anal canal is a separate condition, less common than bowel cancer, and managed differently.

How does Bowel Cancer develop?

Most bowel cancers begin as small, non-cancerous growths on the inner lining of the bowel wall, known as polyps. Polyps are quite common, occurring in roughly 15 to 40 per cent of adults, and the majority are harmless. However, a type called an adenomatous polyp has the potential to become cancerous over time if left undetected. This process is generally slow, unfolding over several years, which is why regular screening provides a meaningful opportunity to find and remove polyps before they progress.

Once a cancerous tumour forms, it can grow deeper into the layers of the bowel wall and eventually spread to nearby lymph nodes. In more advanced cases, the cancer can travel to other organs, most commonly the liver and lungs. These secondary deposits are referred to as metastases.

Risk factors for Bowel Cancer

There is no single cause of bowel cancer, and many people who develop it have no obvious risk factors. That said, certain factors are known to increase a person’s likelihood of developing the disease. Understanding your personal risk can help guide decisions about screening and monitoring.

Age and personal medical history

Risk increases significantly from the age of 45 onwards, with each succeeding decade bringing a higher likelihood of diagnosis. A personal history of bowel polyps, colorectal cancer, inflammatory bowel disease (Crohn’s disease or ulcerative colitis), or type 2 diabetes are all recognised as factors that can elevate risk. People who have previously had certain other cancers, including ovarian or endometrial cancer, may also face an increased risk.

Family history and genetic conditions

Approximately 30 per cent of all bowel cancer cases have a family history or hereditary component. The more family members who have been affected, and the younger they were at diagnosis, the stronger the likelihood of a familial link. Two inherited conditions carry a particularly elevated risk: Lynch syndrome (also known as hereditary non-polyposis colorectal cancer, or HNPCC) and Familial Adenomatous Polyposis (FAP).

Lynch syndrome is the most common cause of hereditary bowel cancer, typically presenting between the ages of 40 and 50 rather than the more typical 60 to 70 years seen in the general population. It is caused by a change in a gene that normally helps protect cells from cancer. The lifetime risk of developing bowel cancer for someone with Lynch syndrome can be as high as 70 to 90 per cent, and the condition is also associated with increased risk of cancers of the uterus, ovaries, kidneys, and other organs. Children of an affected parent have a 50 per cent chance of inheriting the gene. For people with a family history of Lynch syndrome, referral to a Family Cancer Clinic is recommended.

Familial Adenomatous Polyposis is a condition in which hundreds of adenomatous polyps develop in the large bowel, often beginning in adolescence. Without intervention, the risk of these polyps becoming cancerous is extremely high. Treatment typically involves surgery to remove the colon, supported by an experienced specialist team. Regular surveillance with sigmoidoscopy or colonoscopy is recommended from the age of 10 to 15 years for those with a known family history of FAP.

Lifestyle and modifiable risk factors

Several lifestyle factors have been linked to an increased risk of bowel cancer, and addressing these can meaningfully reduce that risk. Diets high in red meat and processed meat are associated with greater risk. The World Cancer Research Fund recommends limiting red meat intake to no more than 500 grams (cooked weight) per week and avoiding processed meats such as bacon, ham, salami, and certain sausages where possible.

Eating a diet rich in wholegrains, vegetables, fruit, legumes, and other high-fibre foods is associated with a lower risk of bowel cancer. Dairy products and calcium are also associated with a reduced risk. Maintaining a healthy body weight, engaging in regular physical activity, limiting alcohol consumption, and not smoking all contribute to lowering risk. Recreational physical activity has been shown to reduce the risk of colon cancer specifically. If you are unsure about dietary changes relevant to your personal situation, a referral to an accredited practising dietitian through the Dietitians Australia Find a Dietitian directory can provide tailored guidance.

Symptoms of Bowel Cancer

In its earliest stages, bowel cancer often produces no symptoms at all. As the cancer progresses, a range of symptoms may appear. It is important to remember that these symptoms are shared by many other bowel conditions, and their presence does not necessarily mean cancer. However, if any of the following have persisted for more than two weeks, they warrant prompt medical review.

Blood in the stool or on the toilet paper, whether bright red or causing the stool to appear dark, should never be dismissed. A persistent or unexplained change in bowel habits, including diarrhoea, constipation, a sense of incomplete emptying, or a change in stool consistency or appearance, are also symptoms worth investigating. Unexplained weight loss, extreme tiredness or fatigue, abdominal pain or bloating, and a lump or swelling in the abdomen are further signs that require assessment by a doctor.

Blood from the bowel can also result from haemorrhoids, anal fissures, diverticular disease, or inflammatory bowel disease. Your GP can help determine whether further investigation is needed, and a referral to a gastroenterologist will allow for a thorough evaluation.

Screening for Bowel Cancer

Screening is the process of testing people who have no symptoms, with the aim of detecting cancer or pre-cancerous changes at a stage when treatment is most effective. Because bowel cancer often develops without early warning signs, screening is one of the most important tools available for reducing the number of deaths from the disease.

The National Bowel Cancer Screening Program

The Australian Government’s National Bowel Cancer Screening Program (NBCSP) offers free bowel cancer screening to eligible Australians aged 45 to 74. People aged 50 to 74 receive a screening test in the mail every two years. Those aged 45 to 49 can request their first kit by contacting the National Cancer Screening Register at ncsr.gov.au or calling 1800 627 701. All eligible people in this age group can also ask their GP about obtaining a test kit.

The test used is a faecal immunochemical test (FIT), which involves collecting small samples from two separate bowel motions and mailing them to a pathology laboratory. Results are sent to both the patient and their GP. A positive result, indicating the presence of blood in the stool, does not confirm cancer; it indicates that further investigation, usually a colonoscopy, is required to determine the cause.

Screening for higher-risk individuals

For people with a personal or family history that places them at higher risk, a standard two-yearly FIT screening program may not be sufficient. A gastroenterologist can assess your individual risk profile and recommend an appropriate screening or surveillance schedule. This may involve colonoscopy at regular intervals, beginning earlier in life than would be recommended for the general population. People with Lynch syndrome, for example, are generally advised to undergo colonoscopy every one to two years from age 25.

How is Bowel Cancer diagnosed?

If your GP has concerns following an assessment of your symptoms or a positive FIT result, you will be referred to a specialist for further investigation. A gastroenterologist is often the first specialist involved, given their expertise in diagnosing and evaluating conditions of the bowel.

Colonoscopy

A colonoscopy is the most thorough diagnostic investigation for bowel cancer. It allows a gastroenterologist to examine the full length of the large bowel, from the rectum to the beginning of the small bowel, using a thin, flexible instrument equipped with a camera and light source. The procedure is performed under sedation, so most patients find it well tolerated.

If anything suspicious is found during the colonoscopy, the specialist can take tissue samples (biopsies) for laboratory analysis. Small polyps can also be removed at the same time. Thorough bowel preparation is essential before the procedure, as an incompletely cleared bowel can cause lesions to be missed. Your specialist will provide detailed preparation instructions in advance.

Flexible Sigmoidoscopy

A flexible sigmoidoscopy examines the rectum and the lower section of the colon, where the majority of polyps and bowel cancers are found. It is performed without sedation and can usually be completed within 30 minutes in an outpatient setting. If further investigation is needed following a sigmoidoscopy, a full colonoscopy may be recommended.

CT Colonography (Virtual Colonoscopy)

CT colonography uses a CT scanner to produce detailed two and three-dimensional images of the colon and rectum, offering a non-invasive alternative for people who are unable to undergo a standard colonoscopy. The bowel must still be prepared and cleared before the procedure, and if any abnormality is detected, a conventional colonoscopy will be needed for biopsy or polyp removal.

Additional investigations

Other tests that may be used during the diagnostic process include blood tests, including those checking for anaemia, CT scans, MRI scans, and PET-CT scans. These investigations help determine whether and how far the cancer has spread, which is essential information for planning treatment. The cancer is staged using the TNM system, which describes the depth of tumour invasion, lymph node involvement, and the presence or absence of metastases.

Treatment for Bowel Cancer

Treatment for bowel cancer is planned by a multidisciplinary team of specialists, including gastroenterologists, colorectal surgeons, medical oncologists, radiation oncologists, and other relevant clinicians. The recommended approach will depend on the location of the cancer, how far it has progressed, and the patient’s overall health and preferences. While a gastroenterologist plays a central role in diagnosis and surveillance, surgical and oncological specialists lead treatment for confirmed cancer.

Surgery

Surgery is the primary treatment for bowel cancer and may be performed as open surgery or through a keyhole (laparoscopic) approach. For colon cancer, the most common procedure is a colectomy, in which the section of bowel containing the cancer is removed along with a margin of healthy tissue on either side. Nearby lymph nodes are also removed and examined for cancer cells. In most cases, the two ends of the remaining bowel are joined back together in a procedure called an anastomosis.

For rectal cancer, the type of surgery depends on how close the tumour is to the anus. When the cancer is sufficiently distant from the anus, it is usually possible to remove it while preserving bowel continuity. When the cancer is very close to the anus, removal of the anus itself may be necessary, which requires a permanent colostomy. Surgery for rectal cancer typically takes two to three hours under general anaesthetic, with a hospital stay of five to ten days. Recovery to full activity generally takes up to three months.

A stoma, an opening in the abdomen through which waste is collected in an external bag, may be required either temporarily or permanently. Improvements in surgical technique mean fewer patients require a permanent stoma than in previous decades. If a stoma is planned, detailed education and support are provided before and after the operation. Visit the Gastrological Society of Australia website to learn more about Life with a Stoma.

Chemotherapy and Radiation Therapy

Chemotherapy may be recommended before surgery to shrink a tumour and make it easier to remove, or after surgery to reduce the likelihood of the cancer returning. In cases where bowel cancer has spread beyond the bowel, chemotherapy may be used as the primary systemic treatment. Radiation therapy is more commonly used for rectal cancer than for colon cancer. It may be given before surgery to reduce tumour size, or after surgery if there is concern about residual disease. When used together, chemotherapy and radiation therapy can increase the sensitivity of cancer cells to radiation.

Targeted and Immunological Therapies

For advanced bowel cancer that has spread to other organs, treatment with targeted therapies or immunotherapy may be an option depending on the specific characteristics of the cancer cells. These systemic treatments work differently from conventional chemotherapy and may be appropriate for a subset of patients identified through genomic testing of the tumour. Your treating oncologist will discuss whether these options are relevant to your situation.

Life after Bowel Cancer treatment

Recovery from bowel cancer treatment varies from person to person, depending on the type and extent of treatment received. Following surgery, most patients are encouraged to begin moving and walking as soon as possible to support recovery. Physical activity, once cleared by the treating team, plays an important role in returning to normal function.

For those who have had a stoma formed, a stoma nurse will provide education and support on caring for it, and specialist support services are available throughout Queensland. Many people adjust well over time, and the majority find that it does not prevent a full and active life.

Treatment for bowel cancer can affect sexual function and fertility, particularly when radiation therapy to the pelvic area is involved. These effects are worth discussing with your specialist before treatment begins.

Regular follow-up with your gastroenterologist and treatment team is important after bowel cancer treatment. Surveillance colonoscopy at recommended intervals helps ensure that any recurrence or new polyps are detected and managed promptly.

The role of your Gastroenterologist

A gastroenterologist is a specialist in the diagnosis and management of conditions affecting the digestive system. In the context of bowel cancer, your gastroenterologist plays a central role in assessing symptoms, performing colonoscopy, identifying polyps and early cancers, coordinating referrals to surgical and oncological colleagues where required, and providing ongoing surveillance after treatment.

If you have risk factors for bowel cancer, such as a family history, a personal history of polyps or inflammatory bowel disease, or symptoms that have persisted for more than two weeks, a specialist assessment is appropriate. Your GP can provide a referral, then you can contact our practice directly to arrange a consultation.

To discuss your referral, bowel health concerns and or to arrange a colonoscopy, contact Queensland Gastroenterology to book a consultation with one of our specialist gastroenterologists. Early assessment and appropriate screening can make a significant difference to outcomes.

This information has been sourced and adapted from education resources developed by the following, as at 21/5/2026:

• Bowel Cancer Australia/
• Faculty of Radiation Oncology, The Royal Australian and New Zealand College of Radiologists (https://www.targetingcancer.com.au/treatment-by-cancer-type/bowel-colon-cancer/)
• Health Direct
• Better Health Channel Victoria (Better Health Channel)
• Gastroenterological Society of Australia