Medical Oncologist
CION Cancer Clinics
Colon cancer symptoms: the complete list, and what usually causes them | CION Cancer Clinics
Colon cancer can cause a lasting change in bowel habit, blood in the stool, tiredness from a low haemoglobin, belly pain and unplanned weight loss. Most people with these symptoms do not have cancer, because piles, infections and irritable bowel are far commoner. This page lists every symptom, what more often explains it, and how long is too long to wait before seeing a doctor. At CION Cancer Clinics, our specialists help you judge which bowel symptoms need tests and plan screening that fits your risk.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed October 2026, next review due October 2027
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On this page
- What are the symptoms of colon cancer?
- Which symptoms can colon cancer cause?
- What happens when you take these symptoms to a clinic?
- Which features point towards a benign cause, and which away from it?
- Four things people tell us about their symptoms, and what is true
- What this page cannot tell you
- Common questions about colon cancer symptoms
The short answer
What are the symptoms of colon cancer?
The symptoms of colon cancer are a lasting change in bowel habit, blood in or on the stool, tiredness from a low haemoglobin, pain or bloating in the belly, and weight loss nobody planned. Every one of these is far more often caused by something that is not cancer. Piles, a fissure, an infection and irritable bowel explain most of what brings people here.
Why the list looks so ordinary
Colon cancer has no symptom of its own. So doctors judge a symptom by how long it has lasted, whether it is new for you, and whether it keeps getting worse. A loose stool for three days after a wedding feast is different from a looser stool every day for two months.
What the pattern usually means
One symptom alone is rarely cancer. Two or three arriving together, in someone over forty or in anyone with a parent or sibling who had bowel cancer, moves the question up the list. Being young does not rule it out, and colon cancer in people in their thirties is being found more often. Youth still makes a benign cause more likely.
This page lists what colon cancer can look like. It cannot tell you whether you have it.The complete list
Which symptoms can colon cancer cause?
They fall into four groups. Most people with cancer have one or two of them, not the whole list.
Changes in how you go
Diarrhoea, constipation or the two alternating, stools that have become narrow, or a feeling you have not emptied fully. A tumour narrowing the bowel is one cause. Diet, medicines, thyroid trouble and irritable bowel are far commoner ones.
Worth a check if
- It has lasted more than a few weeks
- It is new for you, not your lifelong pattern
- Diet changes have not settled it
Blood and mucus
Bright red blood on the paper is usually piles or a fissure. Blood mixed into the stool, dark or maroon blood, or slime with the stool matters more. A tumour on the right side often bleeds where you cannot see it.
Read next
Tiredness and anaemia
A tumour on the right side can leak small amounts of blood for months with no visible change in the stool. The only symptom may be tiredness, breathlessness on stairs or a pale look. Iron-deficiency anaemia, meaning a low haemoglobin from too little iron, in a man or a woman past the menopause is a reason to look at the bowel.
Pain, bloating and weight
Cramping, gas, a bloated belly that does not settle, a lump you can feel, or weight dropping with no change in eating. On their own these are rarely cancer. With a bowel change or bleeding, they add weight to the picture.
Severe pain with vomiting and no wind or stool passing is different. See the box below.Not sure whether this applies to you?
Ask an oncologist
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When to see a doctor, and when not to wait for one
See a doctor this week if a change in bowel habit, bleeding, mucus, tiredness or unexplained weight loss has lasted more than three weeks, or if blood is dark or mixed into the stool. Go to an emergency department today if you have severe belly pain with vomiting and cannot pass wind or stool, if you pass a large amount of blood, or if you feel faint, sweaty and breathless. Those can mean a blocked bowel or heavy bleeding, whatever the cause.
What the doctor will do
What happens when you take these symptoms to a clinic?
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Questions, in more detail than you expect
How long, how often, what colour, whether anyone in the family had bowel cancer or polyps, and whether your weight has changed. Write the answers down before you go.
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An examination of the belly and the back passage
The doctor feels the abdomen and usually examines the rectum with a gloved finger. It finds piles, a fissure and some low tumours. A normal examination does not rule out a problem higher up.
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Blood tests
A full blood count looks for a low haemoglobin and low iron. A CEA test is sometimes added. It is not a cancer test, and a normal CEA is common in early cancer.
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A stool test, sometimes
A FIT looks for hidden blood. It is a screening test, not a diagnosis. A positive result leads to colonoscopy, and a negative one does not close the question while symptoms continue.
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Colonoscopy if anything points to the bowel
A thin camera examines the whole colon and takes a biopsy, a small tissue sample, from anything suspicious. CION arranges it through a partner endoscopy unit. It is the test that settles where a symptom is coming from.
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Side by side
Which features point towards a benign cause, and which away from it?
More often benign
Needs a proper look
Bright red blood on the paper, with pain on passing stool
Dark or maroon blood mixed into the stool, without pain
Loose stools after a change of food, settling within days
A new bowel pattern lasting weeks with no obvious trigger
Tiredness after poor sleep or a busy season
Tiredness with a low haemoglobin on a blood test
Bloating that comes and goes with meals
Bloating that keeps worsening, with weight loss
One symptom, in a younger person, no family history
Several symptoms together, or any symptom with a family history
Commonly believed
Four things people tell us about their symptoms, and what is true
"It is only piles. Everyone in my family gets piles."
Piles are common and often really are the cause. But piles and a tumour can sit side by side, and bleeding blamed on piles for months is a common story behind a late diagnosis. Bleeding that persists deserves one proper examination, even if piles are found.
"There is no pain, so it cannot be anything serious."
Early colon cancer is usually painless. Pain tends to arrive late, when a tumour has grown enough to narrow the bowel. Painless bleeding is exactly the pattern worth checking.
"My stool is normal, so my bowel is fine."
A tumour on the right side of the colon often changes nothing you can see. It shows up as tiredness and a low haemoglobin instead, which is why unexplained anaemia is investigated with a colonoscopy.
"I am too young for colon cancer."
Most younger people with these symptoms have something benign. But cancers in people in their thirties and forties are rising, and they are often found late because everyone assumed age ruled it out.
Being straight with you
What this page cannot tell you
It cannot tell you whether your symptom is cancer. The same bleeding can be a fissure in one person and a tumour in another, and the only way to tell is to look. If this list has worried you, the useful next step is an appointment.
It cannot replace a colonoscopy
Blood tests, a stool test and a normal examination can all be reassuring and still miss a cancer. If cost, embarrassment or fear of the preparation is holding you back from a colonoscopy, tell the doctor. All three can be dealt with.
Who this page does not apply to
Symptoms at the anus itself, such as a lump, itching or pain on passing stool, usually come from piles or a fissure and, rarely, from anal cancer. Cancer in the last part of the bowel has its own hub at rectal cancer. If a colonoscopy has already found something, this page is behind you. Ask the doctor who did it about the next step.
Unsure whether your symptom is worth an appointment? Call the helpline and describe it.Questions we are asked
Common questions about colon cancer symptoms
What is usually the first symptom of colon cancer?
There is no single first symptom. For tumours on the left side it is often a change in bowel habit or visible blood. For tumours on the right it is often tiredness from a low haemoglobin. Many are found by screening before any symptom.
How long should I wait before seeing a doctor?
If a bowel symptom is new and has lasted about three weeks, see a doctor. Dark blood mixed into the stool, unexplained weight loss or anaemia should not wait that long. Severe pain with vomiting and no stool or wind is an emergency today.
Can colon cancer cause symptoms without any bleeding?
Yes. Right-sided tumours often never produce visible blood. The signs are tiredness, a pale look, vague pain or a lump, and sometimes weight loss. Blood may be present in amounts too small to see, which is what a FIT stool test detects.
Are the symptoms different in women and men?
The bowel symptoms are the same. Anaemia in a woman who still has periods is often blamed on them, so the bowel is checked later. In a man, or a woman past the menopause, a low haemoglobin with low iron is looked into promptly.
Does a normal blood test rule out colon cancer?
No. A full blood count can be normal in early cancer, and CEA is not a screening test. Blood tests cannot see the bowel. If symptoms persist, a normal result is a reason to look further.
Which doctor should I see for these symptoms?
A general physician or family doctor is the right first step and can order the blood count and examine you. If the bowel needs looking at, a gastroenterologist does the colonoscopy. An oncologist comes in only if a biopsy shows cancer.
Can stress or diet cause the same symptoms?
Very often. Stress, irregular meals, travel and iron tablets all change bowel habit or stool colour. These settle when the cause is removed. A symptom that stays after you fix the obvious trigger is the one to report.
Should I get screened if I have no symptoms?
Screening is for people with no symptoms, and it is how early cancers and polyps are usually found. If you are in your mid-forties or older, or a parent or sibling had bowel cancer, read the screening page and ask your doctor about a FIT or a colonoscopy.
Your Specialists
Meet CION's colon cancer specialists. Bring your colonoscopy, scan or biopsy report.
Our surgical and medical oncologists plan colon cancer care together: which operation, whether chemotherapy is needed, and the follow-up that comes after.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
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Sources
- American Cancer Society — Colorectal Cancer Signs and Symptoms
- NHS — Symptoms of bowel cancer
- Cancer Research UK — Symptoms of bowel cancer
- NICE — Suspected cancer: recognition and referral
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Early signs of colon cancerWhat the first changes tend to look like, before the obvious onesBlood in stool: what it usually meansThe symptom that brings most people here, explained on its ownHow long should you wait before seeing a doctor?A plain timetable for each symptomDo I have colon cancer?How to think about your own symptoms without panicking
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