Bowel cancer in adults under 50

What has changed

The pattern has shifted over twenty years and it runs against the trend in everyone else. In Australians under 50, bowel cancer cases more than doubled between 2000 and 2024, from around 960 to an estimated 2,045 a year. The incidence rate went from roughly 7 to 12 per 100,000. Over the same period, incidence in people over 50 fell.

The sharpest rise has been in people in their thirties, which is now the only age group in the country where deaths from bowel cancer are still going up. In 2024 bowel cancer was the leading cause of cancer death in Australian men under 50 and the second leading cause in women under 50.

The same thing is happening in North America, Europe and parts of Asia, so it is not an Australian artefact and it is not simply better detection. Diet, obesity, inactivity, alcohol, smoking, early-life antibiotic exposure and changes in gut bacteria have all been proposed, and no single explanation accounts for it. Only about one in six to one in five of these cancers are linked to an inherited syndrome. The majority occur in people with no family history at all.

Why it matters so much that it is found early

Bowel cancer is one of the most curable cancers there is, provided it is found before it spreads. Five-year survival in Australia is around 99 per cent for the earliest stage, 89 per cent at stage II, 71 per cent at stage III and around 13 per cent once it has spread to other organs.

Across studies worldwide, the gap between a young person first reporting symptoms and the diagnosis being made averages about four to six months, and in some groups runs beyond a year. That is roughly twice as long as the wait for someone over 50 with the same symptoms. The cancer does not behave differently in a young person. The pathway to diagnosis does.

The symptoms that should not be waved away

Pooled across 81 studies, rectal bleeding is the commonest first sign in people diagnosed under 50, present in about 45 per cent. Abdominal pain follows at about 40 per cent and a change in bowel habit at about one in four. These are extremely common symptoms with mostly innocent causes, which is exactly why they get attributed to something else. The point is not that every young person with bleeding has cancer. The point is that the assessment should not stop at an assumption.

• Rectal bleeding that is persistent, recurrent or mixed through the stool rather than only on the paper
• A change in bowel habit lasting more than four to six weeks, whether that is looser motions, constipation or a persistent feeling of not having finished
• Iron deficiency anaemia without a clear explanation. In a young woman this is often attributed to periods, and in a young man it is sometimes not chased at all
• Unexplained weight loss or persistent fatigue alongside bowel symptoms
• Abdominal pain that is progressive or that wakes you at night
• A lump felt in the abdomen or found on examination

Four of these have been measured directly. In a large study of adults under 50, rectal bleeding, abdominal pain, diarrhoea and iron deficiency anaemia were the symptoms most closely linked with bowel cancer: having one of them roughly doubled the likelihood compared with having none, and having three or more raised it around sixfold. The rest of the list is not part of that calculation, and still warrants assessment.

That is a shift in probability rather than a diagnosis, and it is enough to justify looking properly.

Why it gets missed

Three things tend to happen, and they compound.

The first is that a plausible benign explanation is found and accepted. Haemorrhoids are present in a large proportion of adults, so a young person with bleeding and visible haemorrhoids has a ready answer, and it may be the right one. It is not, on its own, a reason to stop looking, particularly if the bleeding continues after the haemorrhoids are treated.

The second is that a normal result is read as a clear one. A stool test picks up most established cancers but far fewer early lesions, and in someone with symptoms it was never the right test to settle the question. A negative result in a symptomatic young patient does not overturn the clinical picture.

The third is anatomical, and it is the part that has changed. Research from A/Prof Kariyawasam's group, based on more than 230,000 colonic specimens, found that the flat, pale, mucus-covered lesions known as sessile serrated lesions are being found in progressively younger patients, and that patients under 45 carry several times the odds of having one. These sit in the right-hand side of the colon, they bleed the least of any lesion type and they are the ones most easily missed on a hurried examination. In practical terms, unexplained iron deficiency in a young person matters more than it is usually given credit for, and the thoroughness of the colonoscopy matters more than the fact of having had one.

What to ask for

If you are under 50 and something has not settled, the following are all reasonable to ask.

• A physical examination, including a rectal examination. It is quick, it is under-used and it detects a meaningful proportion of rectal cancers.
• A full blood count and iron studies. Iron deficiency in this setting is a finding, not a footnote.
• A clear plan for review. If the first round of tests is reassuring but the symptom persists, that should trigger escalation rather than a repeat of the same reassurance. Ask when you should come back and what would change the plan.
• A referral for colonoscopy where there is a lump, unexplained iron deficiency, bleeding that has gone on beyond four to six weeks, a positive stool test alongside symptoms or a family history that fits.
• A screening kit from 45, which you have to request until you turn 50. Being well is the point of screening, not a reason to skip it.

None of this means assuming the worst. Most young people with these symptoms do not have cancer. It means that being 34 is not itself a test result.

If someone in your family was diagnosed young

A bowel cancer diagnosed under 50 has implications for the rest of the family, and this is one of the most commonly missed steps after a young diagnosis.

The rule to hold on to is ten years before the age of the youngest person in the family who was diagnosed. First-degree relatives, meaning parents, brothers, sisters and children, are generally advised to begin colonoscopy at that age and then every five years. Where the family history is otherwise unremarkable the start is capped at 50, and where it is stronger at 40, so that nobody starts late. A young diagnosis in the family makes the ten-year rule the one that decides it.

For a family where someone was diagnosed at 34, that gives a starting age of 24. Anyone already past it, which is most parents, should be booked now rather than at some point in the future.

Referral to a familial cancer service is worth raising where anyone in the family was diagnosed under 50, where two or more relatives have been affected or where the tumour testing suggests an inherited syndrome such as Lynch syndrome. There is more on family history and screening intervals on the screening page.

Research on this

The research described above sits inside a larger body of work from A/Prof Kariyawasam's group on how colonic pathology has changed over more than a decade in Western Sydney. It has looked at the rise of serrated lesions in younger patients, the shift in where in the colon significant lesions are found and the effect of socioeconomic disadvantage on what is found and when.

He has published on early-onset bowel cancer and on colonic pathology trends, teaches on the subject for general practice and has commented publicly on the case for taking symptoms in younger patients seriously.

Where younger patients with bowel symptoms are seen in Sydney

A/Prof Viraj Kariyawasam is a consultant gastroenterologist and hepatologist whose work includes bowel cancer screening and prevention. Younger people with bowel symptoms are seen in Norwest, Rouse Hill, Pennant Hills and Macquarie Park.

The colonoscopy is performed at Norwest Private Hospital, Macquarie University Hospital and Pennant Hills Day Surgery. A referral from your GP is needed for a consultation.