Why Symptoms Are Easy to Miss
Bowel cancer is one of the most common cancers in Australia — roughly 1 in 14 people will develop it in their lifetime. One of the most difficult things about the disease is that in its early stages it often causes no symptoms at all. When symptoms do appear, they tend to look like something far more mundane: haemorrhoids, a sensitive bowel, too much coffee, not enough fibre.
This misattribution matters enormously. Bowel cancer caught at Stage I has a five-year survival rate approaching 90%. Caught much later, that figure falls significantly. Taking your symptoms seriously — and getting them checked — is genuinely one of the most important things you can do.
It is equally important to understand that no set of symptoms can definitively diagnose bowel cancer. The only test that can do that is a colonoscopy — a camera examination of the entire large bowel, done under sedation, that lets your specialist look directly at what is happening.
Symptoms That Deserve Attention
Rectal Bleeding
Blood in or on your stool is one of the most important symptoms to report to your GP. Bright red blood on the toilet paper or in the bowl is most often caused by haemorrhoids or an anal fissure — but it can also come from a rectal cancer. Blood that is dark, maroon-coloured, or mixed into the stool itself suggests a source higher up in the bowel and needs urgent investigation. Please do not assume rectal bleeding is haemorrhoids without getting it checked.
A Change in Bowel Habit Lasting More Than Three Weeks
If your bowel habits have changed — and the change has lasted more than three weeks without a clear explanation — it is worth investigating. This includes stools that are looser, more frequent, or harder than usual; stools that are narrower or ribbon-like; or a pattern that alternates between diarrhoea and constipation. Short-lived changes after travel, illness, or a dietary change are normal. A persistent, unexplained change is not something to ignore.
Unexplained Weight Loss
Losing weight without trying — particularly more than 5 kg over a few months — is a red flag that always needs investigation. When it comes to your bowel, a tumour can affect how well your body absorbs nutrients, reduce your appetite, and increase the energy your body uses. If the scales are going down and you are not sure why, please see your GP.
Persistent Abdominal Pain or Cramping
Cramping, bloating, or a feeling of pressure in your abdomen that keeps coming back — particularly in the lower belly — warrants a proper assessment. Pain that wakes you at night or that is slowly getting worse over time is especially important to take seriously. Bowel cancer can cause a partial blockage that leads to cramping and distension.
Persistent Tiredness or Low Iron
Bowel cancers — particularly those on the right side of the colon — can bleed very slowly without producing any visible blood in your stool. Over time, this hidden blood loss leads to iron deficiency anaemia — a condition where your blood does not carry enough oxygen around your body. The symptoms are persistent tiredness, paleness, feeling breathless doing ordinary things, and dizziness. If blood tests have shown your iron is low and there is no obvious explanation, your bowel deserves investigation.
A Feeling of Incomplete Emptying
If you regularly feel like you have not fully emptied your bowel, even straight after going, this is worth mentioning to your GP. This sensation — medically called tenesmus — is commonly associated with rectal cancer. It can feel like a constant pressure or urgency in the back passage. If you have been experiencing this, please do not dismiss it.
Please See Your GP If You Notice Any of These
Please see your GP promptly if you notice any of the following:
• Blood in or on your stools — bright red, dark, or mixed into the stool
• A change in your bowel habit lasting more than 3 weeks without a clear cause
• Unexplained weight loss of more than 5 kg
• Persistent abdominal pain, cramping, or bloating
• Ongoing tiredness with no clear explanation
• Low iron levels found on a blood test
• A feeling that your bowel is never fully empty
These symptoms do not mean you have cancer — most of the time, they have a benign explanation. But they all need proper investigation. A colonoscopy is the test that gives you a definitive answer.
Why You Cannot Diagnose This From Symptoms Alone
Almost every symptom of bowel cancer is also caused by something far more common and benign. Rectal bleeding is most often haemorrhoids. Changes in bowel habit are frequently IBS, diet, or a gut infection. Fatigue has dozens of causes. This overlap is real — and it is part of why bowel cancer can be missed for months.
The important point is that you cannot tell the difference by looking at the symptoms alone. The only investigation that answers the question definitively is a colonoscopy — a camera examination of the entire large bowel, done under sedation. It lets the specialist see the bowel lining directly, take a small tissue sample from anything that looks abnormal, and remove any polyps found.
If your GP thinks your symptoms need investigation, they will refer you to a colorectal surgeon. Please do not delay seeking that referral — earlier investigation always leads to better outcomes.
When Your Symptoms Need Urgent Attention
Most bowel cancer investigations are arranged urgently but not as emergencies. However, some situations need immediate medical attention:
- Heavy rectal bleeding — significant fresh blood loss that is not stopping
- Complete inability to pass stool or wind — this may mean a bowel obstruction
- Severe abdominal pain with swelling — may suggest a perforation or obstruction
- Feeling faint or collapsing — call 000 immediately
For any of these, go to your nearest emergency department or call 000 right away.
What About the Bowel Screening Program?
Australia's National Bowel Cancer Screening Program provides free FOBT test kits every two years to Australians aged 45–74. It is an excellent programme — but it is designed for people without symptoms. If you already have symptoms, please do not wait for your next kit or for it to arrive in the post. Symptomatic patients need direct investigation through a GP and specialist referral, not a home screening test.
Please speak to your GP without delay if you have any of the symptoms described on this page. A referral to a colorectal surgeon can often be arranged the same day you call.
Frequently Asked Questions
It is commonly haemorrhoids — but you should not assume that without seeing your GP. Bright red rectal bleeding can also come from an anal fissure, a polyp, or a rectal cancer. Your GP can examine you and determine whether a colonoscopy is needed. Do not let the most likely explanation prevent you from checking.
As a guide, any change that has lasted more than three weeks without an obvious reason — a change in diet, recent travel, a gut infection — should be assessed by your GP. Do not wait if you also have bleeding or unexplained weight loss alongside the change.
Tiredness has many causes, and most of them are not cancer. But if a blood test has shown low iron or anaemia without a clear explanation, your bowel deserves investigation — especially if you are over 45 or have a family history of bowel cancer. Right-sided colon cancers can bleed so slowly there is no visible blood in your stool at all.
No. Symptoms raise concern, but diagnosis requires a tissue sample taken during a colonoscopy and examined in a pathology lab. Please do not put off seeking investigation because your symptoms seem mild — early bowel cancers often produce only minor, easy-to-dismiss symptoms.
Yes, please. Bowel cancer in younger adults is uncommon but becoming more recognised. Any rectal bleeding should be assessed regardless of your age. In a young person without risk factors, the cause is most likely benign — but that conclusion should come from an examination, not from an assumption.
If your symptoms are convincingly explained by haemorrhoids and there are no other concerning features, your GP may take a watch-and-treat approach initially. However, if your symptoms persist, if you have any red flag features alongside, or if you have a family history of bowel cancer, you should ask for a referral to a colorectal surgeon for proper evaluation.
Have bowel symptoms you are not sure about?
Mr Ba Nguyen is a specialist colorectal surgeon at North Eastern Surgical in Heidelberg. If your GP has recommended a colonoscopy or a specialist review, contact our rooms on (03) 9816 3951 or ask your GP to send a referral to admin@northeasternsurgical.com.au.