Why bowel cancer screening matters
Bowel cancer (also called colorectal cancer) is the second most common cancer in Australia, and the second most common cause of cancer death. Around 15,000 Australians are diagnosed every year, and approximately 5,300 die from it. Those are sobering numbers — but here's the important part: when bowel cancer is caught early, it is highly treatable. The five-year survival rate for stage I (early) bowel cancer is over 90%.
The other good news is that most bowel cancers don't appear out of nowhere. They develop slowly from pre-cancerous growths called polyps, and that process usually takes 10–15 years. That long window is exactly the opportunity that screening is designed to use. Find the polyp early, remove it, and cancer never gets to develop at all.
Recommended timing by patient category
Who should have a colonoscopy and when
- Average risk (no symptoms, no family history): The National Bowel Cancer Screening Program (NBCSP) offers a free bowel cancer test (FOBT — a stool sample test that detects tiny amounts of blood) every two years to Australians aged 45–74. A positive FOBT requires follow-up colonoscopy. Direct colonoscopy screening from age 45 is also now supported for people who prefer a one-step approach — discuss this with your GP.
- One first-degree relative (parent, sibling, or child) diagnosed with bowel cancer: Start colonoscopy screening from age 40–45, or 10 years before the age your relative was diagnosed — whichever comes first. Repeat every 5 years if the result is clear.
- One first-degree relative diagnosed under age 55, or two or more first-degree relatives with bowel cancer: Start from age 40, or 10 years before the youngest relative's diagnosis — whichever comes first. Repeat every 3–5 years.
- Previous bowel polyps (adenomas): Your follow-up interval depends on the number, size, and type of polyps previously found. Typically 1, 3, or 5 years — see our guide to polyp surveillance intervals.
- Inflammatory bowel disease (IBD — Crohn's or ulcerative colitis): Surveillance colonoscopy starting 8 years after your diagnosis, then every 1–3 years depending on how much of your bowel is affected and whether any abnormal cells have been found.
- Lynch syndrome: An inherited condition (also called HNPCC) that significantly raises bowel cancer risk. Colonoscopy from age 25, repeated every 1–2 years. Lifetime bowel cancer risk in Lynch syndrome is 40–80%.
- Familial adenomatous polyposis (FAP): A rare inherited condition in which hundreds of polyps develop in the bowel. Annual flexible sigmoidoscopy or colonoscopy from puberty until surgery to remove the colon is performed. Without surgery, bowel cancer is essentially inevitable.
- Symptoms at any age: If you have symptoms that could indicate a bowel problem, colonoscopy should be arranged promptly — regardless of your age or when you last had one. See the section below on which symptoms to act on.
Average-risk screening: the FOBT and colonoscopy
The National Bowel Cancer Screening Program (NBCSP) sends a free bowel cancer test kit (FOBT) in the post to Australians aged 45–74 every two years. The test involves collecting a small sample from your stool at home to check for tiny amounts of blood — blood that can sometimes indicate a polyp or cancer before any symptoms appear.
A positive FOBT does not mean you have cancer. It means blood was detected, which needs to be investigated further with a colonoscopy. Most positive results turn out to have an innocent explanation — haemorrhoids, a small tear, or a polyp. Of every 100 positive FOBT results, roughly 4–5 will lead to a bowel cancer diagnosis, and around 20 will lead to a polyp being found and removed before it could cause harm. Both outcomes are genuinely worthwhile.
A negative FOBT is reassuring but not a cast-iron guarantee — the test doesn't detect every possible problem. This is why the NBCSP recommends repeating it every two years rather than just once.
If you'd prefer a more direct approach — or if you'd simply rather know for certain — you can discuss going straight to a colonoscopy with your GP. Direct colonoscopy screening from age 45 is now supported by Australian guidelines for people who prefer it.
If you've received an NBCSP kit in the mail and haven't done it yet, please do. Participation rates are lower than they should be, and completing the test really can make the difference between catching something early or missing it.
Symptoms that warrant colonoscopy at any age
Screening recommendations are for people who feel well and have no symptoms. If you do have symptoms, colonoscopy shouldn't wait for a scheduled screening interval — it should be arranged promptly. Please see your GP if any of the following apply to you:
- Rectal bleeding — blood on the toilet paper, in the bowl, or mixed in with your stool. Haemorrhoids are the most common cause, but bowel cancer always needs to be ruled out, especially in people over 45.
- Change in bowel habit — a new pattern of looser stools, constipation, or alternating between the two, lasting more than four weeks.
- Unexplained anaemia — iron deficiency anaemia (low iron levels) without an obvious cause can sometimes be caused by slow, ongoing bleeding from a bowel cancer that isn't visible.
- Unexplained weight loss — losing 5% or more of your body weight over six months without trying or changing your diet.
- A lump in the abdomen — a new mass felt in the belly, particularly towards the lower right side.
- Persistent abdominal pain — new-onset pain that isn't explained by anything else and doesn't settle.
- Mucus in the stool — particularly if it keeps happening and isn't explained by irritable bowel syndrome.
Please don't assume rectal bleeding is just haemorrhoids without seeing a doctor — especially if you're over 45. Haemorrhoids are indeed the most common cause, but bowel cancer needs to be excluded. See your GP promptly if you notice any blood.
Family history: understanding your risk
Your family history is one of the most important factors in deciding when you should start screening. If a first-degree relative — a parent, sibling, or child — has had bowel cancer, your own lifetime risk is approximately double the general population's.
But the details matter:
- One relative diagnosed in their 70s is a different level of risk than one diagnosed at 40.
- Multiple affected relatives — particularly across different generations — raises the possibility of an inherited condition like Lynch syndrome, which needs its own specialist assessment.
- First-degree relatives with bowel polyps (adenomas), especially if they had multiple or large ones, are also worth mentioning when you talk to your doctor.
If you're not sure what your family history means for your own screening, a consultation with Mr Nguyen is a good place to start. He can review your family picture and give you a personalised recommendation rather than a generic one.
Lynch syndrome and hereditary bowel cancer
Lynch syndrome (also called HNPCC — hereditary non-polyposis colorectal cancer) is an inherited condition caused by changes in certain genes that are normally responsible for repairing DNA copying errors (called mismatch repair genes: MLH1, MSH2, MSH6, PMS2). It's the most common cause of inherited bowel cancer and accounts for around 3% of all bowel cancer cases.
People with Lynch syndrome have a lifetime bowel cancer risk of 40–80% and also have an elevated risk of other cancers including uterine, ovarian, stomach, and urinary tract cancers. Because of this, surveillance colonoscopy every one to two years starting from age 25 is strongly recommended. Genetic counselling and testing are available through most major hospitals for families where Lynch syndrome is suspected.
Familial adenomatous polyposis (FAP) is a rarer inherited condition where hundreds to thousands of polyps develop throughout the colon. Without surgery to remove the bowel, bowel cancer is essentially inevitable — which is why early identification and regular surveillance from puberty is so important.
If you have several relatives with bowel cancer or polyps — especially if they were diagnosed young — please raise the possibility of genetic assessment with your GP or with Mr Nguyen. It can make a significant difference for you and your family.
Inflammatory bowel disease and colonoscopy surveillance
If you have inflammatory bowel disease (IBD) — either Crohn's disease affecting the colon, or ulcerative colitis — your risk of bowel cancer is higher than average. The longer you've had active inflammation in the bowel, and the more of the bowel that's affected, the more that risk builds over time.
Surveillance colonoscopy guidelines for people with IBD generally recommend:
- Starting surveillance 8–10 years after your diagnosis
- Repeating every 1–3 years after that — how often depends on the degree of inflammation, whether any dysplasia (abnormal cells) has been found, how much of the bowel is involved, and other risk factors like a family history of bowel cancer
These decisions are made on an individual basis by your specialist. If you have IBD and aren't sure whether you're up to date with surveillance, it's worth checking with your gastroenterologist or colorectal surgeon.
Upper age limit for colonoscopy screening
There's no absolute upper age limit for colonoscopy, but the balance of benefit versus risk does shift as people get older or develop other health conditions. The NBCSP offers the free screening test kit up to age 74, which reflects the evidence that the benefit of routine screening starts to reduce while the risks of sedation and the procedure itself increase in older, frailer patients.
That said, for people in their 70s and 80s who are otherwise in good health, colonoscopy can still be entirely appropriate — for investigating symptoms, or for continuing polyp surveillance where it's recommended. These decisions are always made on an individual basis, taking into account your overall health, your preferences, and what you and your specialist agree makes sense for you.
Frequently asked questions
You're in the right age range for bowel cancer screening. The NBCSP will have sent you an FOBT kit — completing it every two years is the recommended approach for average-risk individuals. If you'd prefer to go directly to a colonoscopy, that's also supported by Australian guidelines. Talk to your GP about what suits you best.
With one first-degree relative diagnosed at 70, the guideline recommendation is colonoscopy from age 40–45, or 10 years before the relative's age at diagnosis (which would be age 60) — whichever comes first. In this case, age 60 is your trigger. Speak to your GP about a referral when you reach that age, or now if you're already there.
A positive FOBT should be followed up with a colonoscopy within 30–60 days — please don't put it off. Most positive results won't turn out to be cancer, but acting promptly means that if there is something significant, it's caught and addressed as early as possible when treatment is most effective.
Two consecutive clear colonoscopies at an average-risk level may mean you can move to a longer interval — potentially 10 years — or return to FOBT screening. Your specialist will guide you on the most appropriate plan based on your age and risk factors at the time.
Yes, please see your GP promptly. Rectal bleeding at any age warrants proper evaluation. Bowel cancer in someone under 40 is uncommon, but it does happen — and the rate of young-onset bowel cancer in Australia is increasing. It may well be nothing serious, but it needs to be checked.
A grandparent is a second-degree relative, which does increase your risk somewhat compared to someone with no family history — but the guidelines are less prescriptive than they are for first-degree relatives. If your grandmother and another relative were both affected, or if there are multiple affected relatives in the family, the picture changes. Discuss your full family history with your GP or Mr Nguyen so it can be assessed properly.
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