Colon cancer warning signs include a lasting change in your bowel habit, blood in or on your stool, abdominal pain or bloating, unexplained weight loss and tiredness caused by anaemia. These symptoms are much more often caused by something harmless, but when they persist they should be checked, because colon cancer found early is easier to treat. This article is part of our guide to cancer surgery and explains seven symptoms to watch for, who is at higher risk and what happens when you get checked.
Early colon cancer often causes no symptoms at all. That is why screening for people over 45, and earlier for those at higher risk, matters as much as knowing the warning signs.
Why colon cancer warning signs are easy to miss
Colon cancer usually grows slowly, often starting as a small growth called a polyp on the inner lining of the bowel. Many polyps never become cancer, but some do over several years.
The early symptoms are common and vague. Bloating, a change in stool or occasional bleeding are easy to blame on diet, stress or hemorrhoids, so people sometimes wait months before mentioning them.
7 colon cancer warning signs not to ignore
The NHS and the American Cancer Society list similar symptoms. Any of the signs below that last for three weeks or more, or keep coming back, are worth discussing with a doctor.
1. A lasting change in bowel habit
Going more often, looser stools, constipation, or alternating between the two, when this is new for you and does not settle, is one of the most common signs. A change in habit matters more than any single day.
2. Blood in or on the stool
Blood may be bright red or make the stool look dark or black. Bright red blood is usually from hemorrhoids or a fissure, but rectal bleeding should be checked rather than assumed to be harmless, especially if you are over 40 or it keeps happening.
3. Abdominal pain, cramps or bloating
Persistent pain, cramping or a bloated feeling, especially if it comes with a change in bowel habit or loss of appetite, can be a sign of a growth in the bowel.
4. A feeling that the bowel has not emptied
Needing to go again soon after you have just been, or feeling that you never quite finish, is called tenesmus. It is more typical of a cancer low in the bowel or rectum.
5. Unexplained weight loss
Losing weight without trying, especially with poor appetite, is a general warning sign for several cancers, including colon cancer. It always deserves a medical check.
6. Tiredness, breathlessness or pale skin
Slow, hidden bleeding from a bowel cancer can cause iron-deficiency anaemia. You may feel unusually tired, short of breath or dizzy, sometimes before any bowel symptoms appear.
7. A lump in the abdomen or rectum
Occasionally a doctor or patient can feel a lump in the tummy or in the back passage. Any new lump should be examined.
Signs that need emergency care
Sometimes colon cancer first shows itself by blocking the bowel. Seek emergency care for severe abdominal pain with swelling, vomiting and being unable to pass wind or stool.
Heavy bleeding from the bottom, black tarry stools with dizziness, or fainting also need urgent assessment the same day.
Who is at higher risk of colon cancer?
Anyone can develop colon cancer, but some factors raise the risk. Age is the biggest, with most cases occurring after 50, although cases in younger adults are rising.
Other risk factors include:
- A close relative with bowel cancer, or an inherited syndrome such as Lynch syndrome
- Previous bowel polyps
- Long-standing ulcerative colitis or Crohn’s disease affecting the colon
- Obesity, smoking, heavy alcohol use and physical inactivity
- A diet high in red and processed meat and low in fibre
- Type 2 diabetes
Having a risk factor does not mean you will develop cancer. It means your doctor may suggest earlier screening or more frequent checks.
How colon cancer is diagnosed
Your doctor will ask about your symptoms and family history and examine your abdomen, often with a rectal examination. Blood tests can show anaemia, and a stool test may look for hidden blood.
The key test is a colonoscopy: a thin, flexible camera passed through the back passage to look at the whole colon. Any suspicious area can be sampled (biopsied) and many polyps can be removed during the same test. If cancer is found, a CT scan helps show whether it has spread.
Screening when you have no symptoms
The American Cancer Society recommends that people at average risk begin regular screening at age 45. Options include a stool-based test at regular intervals or a colonoscopy every few years, depending on the test and the results.
Screening can find cancer before symptoms appear and can prevent it by removing polyps early. If you have a strong family history, ask your doctor whether you should start sooner.
What happens after a diagnosis
Treatment depends on where the cancer is and how far it has spread. For most colon cancers that have not spread widely, surgery to remove the affected part of the bowel with its lymph nodes is the main treatment, sometimes with chemotherapy before or after.
Many operations can be done by keyhole surgery, with a faster recovery for suitable patients. Treatment is usually planned by a multidisciplinary team of surgeons, oncologists, radiologists and pathologists, and you can read how the operation and recovery work on our colorectal cancer surgery page.
Do not wait because of embarrassment
Talking about bowel habits or bleeding can feel awkward, but surgeons and doctors discuss these symptoms every day. Most people who get checked will be told the cause is benign, and those who are not benefit from an earlier diagnosis.
If a symptom on this list has lasted three weeks or more, or you are simply worried, book an assessment. Peace of mind is a perfectly good reason to see a doctor.