Colorectal (bowel) cancer
A cancer of the large bowel (colon or rectum), among the most common cancers but also one of the most preventable and treatable when found early. It usually grows slowly from benign polyps, which screening can detect and remove — and early bowel cancer is very often curable.
What it is
Colorectal cancer, also called bowel cancer, develops in the colon or rectum, the last part of the digestive tract. It is one of the most common cancers, but it is also one where early detection makes an enormous difference: it usually develops slowly over years from small benign growths called polyps, and screening (stool tests and colonoscopy) can find and remove these before they ever become cancer, or catch cancer at an early, highly treatable stage. Early bowel cancer often causes no symptoms; when they appear, they include a persistent change in bowel habit (looser stools, more frequent motions, or constipation lasting weeks), blood in the stool or bleeding from the back passage, abdominal pain or bloating, a feeling of incomplete emptying, unexplained weight loss, or an unexplained iron-deficiency anaemia found on blood tests. Risk rises with age and is influenced by family history, certain inherited conditions, inflammatory bowel disease, and lifestyle factors. Diagnosis is made by colonoscopy and biopsy, not by a blood test. Treatment — surgery, and where needed chemotherapy and radiotherapy — is very effective in early disease, and outcomes are excellent when it is caught early. The tumour marker CEA is used mainly to monitor after diagnosis, not to screen.
Key lab markers
- CEA — the main tumour marker in colorectal cancer, used to monitor after diagnosis and detect recurrence; not a screening test.
- CA 19-9 — sometimes followed alongside CEA.
- Full blood count / ferritin — an unexplained iron-deficiency anaemia can be an early clue and prompts bowel investigation.
- Faecal occult blood / FIT — a screening stool test for hidden blood, not a blood marker.
- Diagnosis is by colonoscopy and biopsy — not by any blood test.
Symptoms
- A persistent change in bowel habit (looser, more frequent stools or new constipation) lasting weeks
- Blood in the stool or bleeding from the back passage
- Abdominal pain, cramping or bloating
- A feeling that the bowel does not empty completely
- Unexplained weight loss
- Tiredness and unexplained iron-deficiency anaemia
- Often no symptoms early — found on screening
Related symptoms
When to discuss with a doctor
A persistent change in bowel habit, blood in the stool, unexplained weight loss, or an unexplained iron-deficiency anaemia — especially over the age of 50, or younger with a strong family history — should be assessed by a doctor without delay, even though most such symptoms have benign causes like haemorrhoids or diet. Take part in bowel screening when invited: stool tests and colonoscopy can remove pre-cancerous polyps and catch cancer early, when it is very often curable. Colorectal cancer is diagnosed by colonoscopy and biopsy, not by a blood test, and CEA is used to monitor after diagnosis rather than to find cancer. Mediora.AI can flag an unexplained iron-deficiency pattern or show a CEA trend in context, but persistent bowel-habit change or bleeding needs specialist assessment; the diagnosis and care belong with your medical team.