Medically reviewed by Prof. Dr. Zahid Mahmood, MBBS, FCPS — General, Laparoscopic & Laser Surgeon, Lahore.
Colorectal cancer, also called bowel cancer, develops in the colon or rectum. Many cases begin as non-cancerous polyps that gradually acquire abnormal changes. Detecting and removing these polyps can prevent cancer, while diagnosing established cancer at an early stage greatly improves the chance of cure.
Warning symptoms include blood in the stool, a persistent change in bowel habit, unexplained iron-deficiency anaemia, abdominal pain, weight loss and fatigue. These symptoms commonly have non-cancerous causes, but they should not be dismissed without appropriate assessment.
What are the colon and rectum?
The colon is the main part of the large intestine. It absorbs water and salts from digested food and forms stool. The rectum is the final section, where stool is stored before passing through the anus.
Colon and rectal cancers share many features but differ in local anatomy and treatment. Colon cancer is commonly treated with surgery followed by chemotherapy when indicated. Rectal cancer may require pelvic MRI, radiotherapy or chemotherapy before surgery, and careful consideration of bowel continuity and stoma formation.
How does colorectal cancer develop?
Most colorectal cancers are adenocarcinomas arising from gland-forming cells in the bowel lining. Many develop through an adenoma–carcinoma sequence: a benign adenomatous polyp grows, accumulates genetic changes and may eventually become invasive cancer.
Not every polyp becomes cancer. Risk is higher in larger polyps, those with advanced microscopic features and certain flat or serrated lesions. Colonoscopy can interrupt this process by removing precancerous growths.
Risk factors
Colorectal cancer can occur without an obvious cause. Risk increases with:
- Increasing age, although rates are rising among some younger adults
- A personal history of colorectal polyps or cancer
- A first-degree relative with colorectal cancer, particularly at a young age
- Inherited syndromes such as Lynch syndrome or familial adenomatous polyposis (FAP)
- Long-standing ulcerative colitis or Crohn’s colitis
- Smoking and excess alcohol
- Obesity, physical inactivity and type 2 diabetes
- A diet high in processed meat and low in fibre-rich plant foods
Having one or more risk factors does not mean cancer is inevitable. Conversely, a healthy lifestyle cannot completely remove risk.
Symptoms of colorectal cancer
Possible symptoms include:
- Bright-red or dark blood mixed with or coating the stool
- A persistent change to diarrhoea, constipation or alternating bowel habits
- Feeling that the bowel has not emptied completely
- Narrower stools or increasing difficulty passing stool
- Persistent abdominal cramps, pain, bloating or swelling
- Unexplained weight loss or reduced appetite
- Fatigue, breathlessness or weakness from iron-deficiency anaemia
- A lump in the abdomen or rectum
Right-sided colon cancer may bleed slowly and present with anaemia, tiredness or weight loss without visible blood. Left-sided or rectal tumours more often cause visible bleeding, altered stool pattern or obstruction.
When should you seek urgent care?
Arrange prompt medical assessment for persistent rectal bleeding, an unexplained change in bowel habit, iron-deficiency anaemia or progressive weight loss—even if haemorrhoids are already known.
Go to an emergency department for:
- Severe abdominal pain with progressive swelling
- Repeated vomiting with inability to pass stool or wind
- Heavy rectal bleeding, fainting or marked weakness
- A rigid abdomen, fever or sudden worsening pain
These can indicate bowel obstruction, perforation or major bleeding and may require emergency treatment.
Haemorrhoids or colorectal cancer?
Haemorrhoids commonly produce fresh red blood after a bowel movement, but the appearance of blood alone cannot safely determine its source. Cancer and haemorrhoids can also occur together.
Bleeding accompanied by a change in bowel habit, anaemia, weight loss, abdominal symptoms or a family history deserves full evaluation. Persistent bleeding should not be repeatedly attributed to piles without examining the colon and rectum when indicated.
Colorectal cancer screening
Screening tests people who have no symptoms. It can detect cancer earlier and find precancerous polyps before they become malignant. Available methods include:
- FIT: a faecal immunochemical test detects tiny amounts of human blood in a stool sample.
- Colonoscopy: directly examines the entire colon and allows biopsy or polyp removal.
- CT colonography: creates detailed images of the bowel after preparation; an abnormal result still requires colonoscopy.
- Flexible sigmoidoscopy: examines the rectum and lower colon.
Starting age and testing interval differ between countries and according to personal risk. People with symptoms need diagnostic assessment rather than waiting for a routine screening test. Those with a strong family history, inflammatory bowel disease or an inherited syndrome require an earlier, personalised surveillance plan.
What does a positive FIT mean?
A positive FIT does not prove cancer. Blood may come from polyps, haemorrhoids, inflammation or another bowel condition. It means colonoscopy or another appropriate investigation is needed.
A negative FIT also does not completely exclude cancer in a symptomatic patient. Continued or worsening symptoms require clinical review.
Clinical assessment
The clinician asks about bleeding, bowel habit, pain, weight, appetite, medicines and family history. Examination may include the abdomen, lymph nodes and a digital rectal examination. A rectal examination can identify a low tumour but cannot assess the remainder of the colon.
Blood tests commonly include a full blood count, iron studies, kidney and liver function and, after diagnosis, carcinoembryonic antigen (CEA) as a baseline tumour marker.
Colonoscopy and biopsy
Colonoscopy is the main test for suspected colorectal cancer. After bowel preparation, a flexible camera is passed through the anus to inspect the rectum and colon. Suspicious tissue is sampled for histopathology, and other polyps can often be removed at the same time.
Risks include bleeding, sedation-related problems and, rarely, bowel perforation. If a tumour prevents the camera from passing or colonoscopy is unsuitable, CT colonography may examine the remaining colon.
What does the biopsy show?
The pathologist confirms whether cancer is present and its type and grade. Tumour tissue is usually tested for mismatch-repair proteins or microsatellite instability. This can suggest Lynch syndrome, provide prognostic information and guide immunotherapy in advanced disease.
Advanced cancers may also be tested for changes such as RAS, BRAF, HER2 or other molecular markers to select targeted treatment. Genetic counselling is recommended when inherited risk is suspected.
How is colorectal cancer staged?
Staging describes how far the cancer has spread:
- Stage I: cancer is limited to the bowel wall.
- Stage II: cancer has grown through the bowel wall but not reached regional lymph nodes.
- Stage III: regional lymph nodes contain cancer.
- Stage IV: cancer has spread to distant organs or the peritoneum.
CT of the chest, abdomen and pelvis is standard for staging. Rectal cancer also requires pelvic MRI to show the tumour’s depth, lymph nodes, relationship to the mesorectal fascia and sphincters. Selected patients may need liver MRI or PET-CT.
Treatment planning
A colorectal multidisciplinary team reviews the colonoscopy, biopsy, scans, medical fitness and patient preferences. The plan differs for colon and rectal cancer and should consider cure, bowel function, treatment burden and quality of life.
Surgery for colon cancer
Surgery is the main treatment for localised colon cancer. The surgeon removes the segment containing the tumour together with its blood supply, mesentery and draining lymph nodes. The healthy bowel ends are usually joined with an anastomosis.
Operations include right or left hemicolectomy, sigmoid colectomy and other segmental resections based on tumour location. Laparoscopic or robotic surgery may be suitable and can reduce wound pain and shorten recovery while following the same cancer-removal principles as open surgery.
Treatment of rectal cancer
Very early, carefully selected rectal cancers may be removed locally through the anus. Most invasive rectal cancers require removal of the rectum and its surrounding mesorectal tissue, called total mesorectal excision.
Depending on MRI stage and location, radiotherapy and chemotherapy may be given before surgery to reduce recurrence and treat microscopic disease. Some patients receive total neoadjuvant therapy, delivering chemotherapy and radiotherapy before the operation.
A low anterior resection preserves the anus and joins colon to the remaining rectum or anal canal. An abdominoperineal resection removes the rectum and anus when adequate cancer clearance or useful sphincter function cannot be preserved, resulting in a permanent colostomy.
Will I need a stoma?
Not everyone requires a stoma. A temporary loop ileostomy may protect a low rectal anastomosis while it heals and can often be reversed later. A permanent colostomy may be necessary when the anus and sphincters are removed, or when joining the bowel is unsafe.
Before planned surgery, a specialist stoma nurse explains appliances, marks the best site and provides practical and psychological support. Modern stoma systems allow most people to return to work, exercise, travel and normal social life.
Emergency presentation
A tumour can obstruct or perforate the bowel. Emergency treatment may involve resuscitation, antibiotics, surgery and temporary or permanent stoma formation. In selected left-sided obstruction, an expandable colonic stent can relieve blockage as a bridge to planned surgery or as palliation.
Chemotherapy
After colon surgery, chemotherapy is routinely considered for stage III disease and selected high-risk stage II cancers. Common regimens use fluoropyrimidines such as capecitabine or 5-FU, often combined with oxaliplatin. The exact duration depends on stage, recurrence risk, fitness and side effects.
Possible side effects include fatigue, nausea, diarrhoea, mouth soreness, infection risk and numbness or tingling from oxaliplatin. Treatment is adjusted to balance benefit with quality of life.
Advanced or metastatic colorectal cancer
The liver and lungs are common sites of spread. Metastatic disease is not automatically untreatable. Selected liver or lung metastases can be removed, ablated or treated with focused radiotherapy, sometimes after chemotherapy, with potential for long-term control or cure.
For more widespread disease, systemic treatment may include chemotherapy, targeted biological drugs and immunotherapy based on the tumour’s molecular profile. MSI-high or mismatch-repair-deficient cancers can respond particularly well to immune checkpoint inhibitors.
Recovery after colorectal surgery
Enhanced recovery programmes encourage early walking, breathing exercises, pain control with fewer sedating medicines and eating as tolerated. Hospital stay varies with the operation, age, fitness and complications.
Bowel function may be irregular for weeks or months. After rectal surgery, some people experience urgency, frequent stools, clustering or leakage—called low anterior resection syndrome. Dietetic advice, medicines, pelvic-floor rehabilitation and specialist follow-up can help.
Possible complications of surgery
- Bleeding, wound or abdominal infection
- Blood clots and chest complications
- Temporary bowel paralysis
- Anastomotic leak from the bowel join
- Injury to nearby organs, nerves or urinary structures
- Urinary or sexual dysfunction after pelvic surgery
- Stoma complications or bowel obstruction from adhesions
Seek urgent advice after discharge for fever, increasing abdominal pain or swelling, persistent vomiting, inability to pass stool or wind, wound discharge, heavy bleeding, breathing difficulty or a painful swollen calf.
Follow-up after treatment
Follow-up aims to identify treatable recurrence, new polyps, a second bowel cancer and treatment-related problems. It may include clinic review, CEA blood tests, CT imaging and follow-up colonoscopy. The schedule depends on stage, treatment and local guidance.
New symptoms between appointments should be reported rather than saved for the next routine visit.
Can colorectal cancer be prevented?
Risk can be reduced by participating in screening, maintaining a healthy weight, remaining physically active, avoiding tobacco, limiting alcohol and eating a diet rich in fibre, whole grains, fruits and vegetables while limiting processed meat.
Do not start aspirin solely to prevent bowel cancer without medical advice; bleeding risks can outweigh benefit. People with Lynch syndrome may be advised to use aspirin under specialist supervision.
Common questions
Does blood in the stool always mean cancer?
No. Haemorrhoids, fissures, inflammation and diverticular disease are common causes. Persistent or unexplained bleeding still requires assessment.
Can young adults develop colorectal cancer?
Yes. Risk is higher with age, but younger adults can be affected. Warning symptoms should be investigated regardless of age.
Does a normal CEA exclude cancer?
No. CEA is not a screening or definitive diagnostic test. Some colorectal cancers do not raise it, while smoking and benign conditions can increase it.
Is colonoscopy painful?
Patients may feel pressure, bloating or cramps. Sedation and pain relief are available, and the endoscopy team adjusts the procedure to comfort and safety.
Can colorectal cancer be cured?
Yes, especially when detected early and completely removed. Some patients with limited liver or lung spread can also achieve long-term survival after combined treatment.
Will bowel habits return to normal?
Many people establish a satisfactory new pattern, but frequency, urgency and stool consistency may change after surgery—particularly following rectal treatment. Specialist support can improve symptoms.
Key message
Blood in the stool, persistent bowel-habit change, unexplained iron-deficiency anaemia, abdominal symptoms and weight loss deserve proper assessment. Screening can prevent colorectal cancer by finding and removing polyps. Colonoscopy with biopsy confirms the diagnosis, while CT and pelvic MRI guide stage-specific treatment with surgery, chemotherapy, radiotherapy or targeted medicines.
Medical references
- O’Connell PR, McCaskie AW, Sayers RD, editors. Bailey & Love’s Short Practice of Surgery. 28th ed. Chapter 77: The large intestine, pp. 1358–1365.
- National Institute for Health and Care Excellence. Colorectal cancer (NG151). Last reviewed April 2026.
- World Health Organization. Colorectal cancer fact sheet. Updated February 2026.
- National Cancer Institute. Colon Cancer Treatment (PDQ®)—Patient Version.
- National Cancer Institute. Colorectal Cancer Screening Tests.
This article provides general education and does not replace an examination or individual cancer advice. Seek emergency care for severe abdominal pain and swelling, repeated vomiting, inability to pass stool or wind, fainting or heavy rectal bleeding.