Colon cancer is a malignant tumour arising from the epithelial lining of the colon and is one of the most common gastrointestinal cancers worldwide. Together with rectal cancer, it forms part of the spectrum of colorectal cancer (CRC). Most colon cancers develop gradually from adenomatous polyps through a sequence of genetic and molecular changes that lead to malignant transformation.

Approximately 90–95% of colon cancers are adenocarcinomas, originating from glandular epithelial cells of the colonic mucosa. Less common histological types include mucinous adenocarcinoma, signet-ring cell carcinoma, neuroendocrine tumours, lymphoma, and gastrointestinal stromal tumours.

Colon cancer is often asymptomatic during its early stages and may only become clinically apparent when the disease is advanced. Early detection through screening significantly improves outcomes and reduces mortality.

Management depends on tumour stage, location, molecular characteristics, and patient fitness. Surgical resection is the primary treatment for localized disease, while chemotherapy and targeted therapies are used in adjuvant and metastatic settings.

Epidemiology

Colon cancer is among the leading causes of cancer-related morbidity and mortality worldwide.

Epidemiological characteristics include:

• Incidence increases with age.

• Most cases occur after 50 years of age.

• Slightly more common in males.

• Incidence is increasing in many developing countries due to changes in diet and lifestyle.

• Adenocarcinoma accounts for approximately 90–95% of cases.

The burden of disease is increasing globally because of:

• Population ageing.

• Obesity.

• Sedentary lifestyle.

• Western dietary patterns.

Risk factors

Several factors increase the risk of colon cancer.

1. Increasing age

• Risk rises significantly after 50 years of age.

2. Genetic and hereditary syndromes

Examples include:

• Familial adenomatous polyposis (FAP).

• Lynch syndrome (Hereditary Non-Polyposis Colorectal Cancer).

• MUTYH-associated polyposis.

3. Personal or family history

• Previous colorectal cancer.

• Previous adenomatous polyps.

• First-degree relative with colorectal cancer.

4. Dietary factors

Increased risk is associated with:

• High intake of red meat.

• High intake of processed meat.

• Low dietary fibre.

• Low fruit and vegetable consumption.

5. Smoking

Long-term tobacco use contributes to colorectal carcinogenesis.

6. Alcohol abuse

Heavy alcohol consumption increases the risk of colon cancer.

7. Obesity and physical inactivity

Obesity promotes:

• Insulin resistance.

• Chronic inflammation.

• Increased cellular proliferation.

8. Inflammatory bowel disease

Particularly:

• Ulcerative colitis.

• Crohn’s colitis.

Risk increases with duration and extent of disease.

9. Type 2 diabetes mellitus

Associated with increased colorectal cancer risk through metabolic and inflammatory pathways.

Pathophysiology

Most colon cancers develop through the adenoma-carcinoma sequence, involving progressive genetic alterations.

The pathway generally includes:

1. Normal colonic mucosa.

2. Adenomatous polyp formation.

3. Dysplasia.

4. Carcinoma in situ.

5. Invasive adenocarcinoma.

Common molecular abnormalities include:

• APC gene mutations.

• KRAS mutations.

• TP53 mutations.

• Microsatellite instability.

Tumour progression occurs through:

• Local bowel wall invasion.

• Lymphatic spread to regional lymph nodes.

• Hematogenous spread.

Common metastatic sites include:

• Liver.

• Lung.

• Peritoneum.

• Bone.

The liver is the most common site of distant metastasis because venous drainage from the colon enters the portal circulation.

Clinical presentation

Early-stage colon cancer may be asymptomatic.

Clinical manifestations vary according to:

• Tumour location.

• Tumour size.

• Presence of obstruction.

• Presence of metastases.

Right-sided and left-sided colon cancers often present differently due to differences in bowel anatomy.

Symptoms

Altered bowel habits

Patients may report:

• Constipation.

• Diarrhoea.

• Alternating constipation and diarrhoea.

Gastrointestinal bleeding

May present as:

• Occult blood loss.

• Blood mixed with stool.

• Dark stools.

Abdominal symptoms

• Abdominal discomfort.

• Colicky abdominal pain.

• Abdominal distension.

• Bloating.

Obstructive symptoms

Particularly in left-sided tumours:

• Constipation.

• Failure to pass stool.

• Failure to pass flatus.

• Intestinal obstruction.

Constitutional symptoms

• Unexplained weight loss.

• Fatigue.

• Loss of appetite.

• General weakness.

Symptoms of advanced disease

• Jaundice from liver metastases.

• Respiratory symptoms from lung metastases.

• Bone pain due to skeletal metastases.

Clinical signs

General findings

• Pallor due to chronic blood loss.

• Cachexia.

• Weight loss.

Abdominal findings

• Abdominal mass.

• Abdominal tenderness.

• Distension.

• Signs of bowel obstruction.

Digital rectal examination findings

Although primarily useful for rectal pathology, digital rectal examination may reveal:

• Occult blood.

• Synchronous rectal lesions.

Signs of metastatic disease

• Hepatomegaly.

• Ascites.

• Supraclavicular lymphadenopathy.

• Respiratory findings due to pulmonary metastases.

Differential diagnosis

Differential diagnoses include:

• Colonic polyps.

• Diverticular disease.

• Inflammatory bowel disease.

• Irritable bowel syndrome.

• Intestinal tuberculosis.

• Colonic lymphoma.

• Hemorrhoids.

• Infectious colitis.

• Ischaemic colitis.

Diagnostic criteria

Colon cancer should be suspected in patients presenting with:

• Persistent change in bowel habits.

• Unexplained iron deficiency anaemia.

• Gastrointestinal bleeding.

• Positive stool occult blood test.

• Unexplained weight loss.

• Abdominal mass.

• Features of bowel obstruction.

Definitive diagnosis requires:

• Colonoscopic visualization of a lesion.

• Histological confirmation from biopsy.

Investigations

Laboratory investigations

Full blood count (FBC)

Used to assess:

• Iron deficiency anaemia.

• Baseline treatment status.

Renal function tests (RFTs)

Includes:

• Urea.

• Creatinine.

Required before contrast imaging and chemotherapy.

Liver function tests (LFTs)

Useful for:

• Detection of liver involvement.

• Baseline treatment assessment.

Carcinoembryonic antigen (CEA)

Used for:

• Baseline assessment.

• Monitoring treatment response.

• Surveillance after treatment.

Stool occult blood test

Useful for:

• Detecting occult gastrointestinal bleeding.

• Screening.

Imaging investigations

Chest X-ray (CXR)

Used to assess:

• Pulmonary metastases.

Double-contrast barium enema

May demonstrate:

• Filling defects.

• Mucosal irregularity.

• Obstructing lesions.

Abdominal and pelvic ultrasound

Useful for:

• Detection of liver metastases.

• Initial abdominal assessment.

CT scan of abdomen and pelvis

Used for:

• Local staging.

• Detection of lymph node involvement.

• Identification of distant metastases.

Endoscopic investigations

Sigmoidoscopy

May identify distal colonic lesions.

Colonoscopy

Preferred investigation because it:

• Evaluates the entire colon.

• Detects synchronous lesions.

• Allows tissue biopsy.

Clinical examination

Digital rectal examination

Recommended as part of colorectal evaluation.

May identify:

• Occult blood.

• Associated rectal pathology.

Histopathology

Biopsy confirms:

• Adenocarcinoma.

• Histological subtype.

• Tumour grade.

Staging

Colon cancer is staged using the TNM staging system.

T – Primary tumour

Determined by:

• Depth of bowel wall invasion.

• Extension into adjacent structures.

N – Regional lymph nodes

Determined by:

• Number of involved lymph nodes.

M – Distant metastases

Assessment of spread to:

• Liver.

• Lung.

• Peritoneum.

• Bone.

Staging determines prognosis and treatment strategy.

Management

Management should follow a multidisciplinary approach involving:

• General or colorectal surgeons.

• Medical oncologists.

• Gastroenterologists.

• Pathologists.

• Radiologists.

Management pathway:

1. Confirm diagnosis.

2. Stage disease.

3. Assess surgical fitness.

4. Perform curative surgery where feasible.

5. Administer adjuvant chemotherapy when indicated.

6. Treat metastatic disease with systemic therapy.

7. Conduct long-term surveillance.

Non-pharmacological treatment

Surgical treatment

Surgery is the primary treatment for non-metastatic colon cancer.

Curative resection

Procedures depend on tumour location and include:

• Right hemicolectomy.

• Left hemicolectomy.

• Extended hemicolectomy.

• Sigmoid colectomy.

All procedures should include:

• Adequate surgical margins.

• Regional lymph node dissection.

Management of intestinal obstruction

May require:

• Emergency surgery.

• Diversion procedures.

• Stenting in selected patients.

Supportive care

Includes:

• Nutritional support.

• Symptom control.

• Psychosocial support.

Pharmacological treatment

Adjuvant chemotherapy

Used following curative surgery for patients with high-risk stage II disease and stage III disease.

Regimen 1 (FOLFOX)

Oxaliplatin – 85 mg/m² – intravenous infusion over 2 hours – day 1ANDLeucovorin – 400 mg/m² – intravenous infusion over 20 minutes – day 1AND5-Fluorouracil (5-FU) – 400 mg/m² – intravenous bolus – day 1

followed by:

5-Fluorouracil (5-FU) – 1200 mg/m²/day – continuous intravenous infusion – days 1–2 (using infusion pump)

Frequency:

• Every 14 days.

Duration:

• 6–12 cycles.

Regimen 2 (CAPEOX/XELOX)

Oxaliplatin – 130 mg/m² – intravenous infusion over 2 hours – day 1ANDCapecitabine – 1000 mg/m² – oral – every 12 hours – day 1 to day 14

Frequency:

• Every 21 days.

Duration:

• 4–8 cycles.

Regimen 3

Capecitabine – 1000 mg/m² – oral – every 12 hours – day 1 to day 14

Frequency:

• Every 21 days.

Duration:

• 6 cycles.

Management of metastatic

disease

Regimen 1 (FOLFOX-based)

Oxaliplatin – 85 mg/m² – intravenous infusion over 2 hours – day 1ANDLeucovorin – 400 mg/m² – intravenous infusion over 20 minutes – day 1AND5-Fluorouracil – 400 mg/m² – intravenous bolus – day 1

followed by:

5-Fluorouracil – 1200 mg/m²/day – continuous intravenous infusion – days 1–2

Frequency:

• Every 14 days.

Duration:

• 6–12 cycles.

May be combined with:

Bevacizumab – 5 mg/kg – intravenous infusion over 1 hour – day 1

OR

Cetuximab – 500 mg/m² – intravenous infusion over 2 hours – day 1

Regimen 2 (CAPEOX)

Oxaliplatin – 130 mg/m² – intravenous infusion over 2 hours – day 1ANDCapecitabine – 1000 mg/m² – oral – every 12 hours – day 1 to day 14

Frequency:

• Every 21 days.

Duration:

• 4–8 cycles.

May be combined with:

Bevacizumab – 5 mg/kg – intravenous infusion over 1 hour – day 1

Regimen 3

Capecitabine – 1000 mg/m² – oral – every 12 hours – day 1 to day 14

Frequency:

• Every 21 days.

Duration:

• 6 cycles.

Management according to underlying cause

Non-metastatic colon cancer

Management:

1. Surgical resection with lymph node dissection.

2. Histopathological staging.

3. Adjuvant chemotherapy where indicated.

4. Surveillance with CEA and colonoscopy.

Locally advanced colon cancer

Management:

• Surgical resection.

• Adjuvant chemotherapy.

• Multidisciplinary assessment for high-risk disease.

Metastatic colon cancer

Management:

• Combination chemotherapy.

• Targeted therapy where appropriate.

• Surgical resection of selected metastatic lesions.

• Palliative care for advanced disease.

Referral

All patients with suspected or confirmed colon cancer should be referred to specialized oncology or colorectal surgery centres.

Urgent referral indications

• Intestinal obstruction.

• Significant gastrointestinal bleeding.

• Severe anaemia.

• Rapid weight loss.

• Palpable abdominal mass.

• Suspected metastatic disease.

Complications

Disease-related complications

• Intestinal obstruction.

• Bowel perforation.

• Gastrointestinal bleeding.

• Severe anaemia.

• Liver metastases.

• Lung metastases.

• Peritoneal carcinomatosis.

Treatment-related complications

Surgery

• Anastomotic leak.

• Surgical site infection.

• Intra-abdominal abscess.

Chemotherapy

• Neutropenia.

• Mucositis.

• Peripheral neuropathy (oxaliplatin).

• Diarrhoea.

Targeted therapy

Bevacizumab

• Hypertension.

• Bleeding.

• Delayed wound healing.

Cetuximab

• Acneiform skin rash.

• Infusion reactions.

Prognosis

Prognosis depends on:

• TNM stage.

• Lymph node involvement.

• Presence of metastases.

• Completeness of tumour resection.

• Response to chemotherapy.

Patients diagnosed with localized disease have significantly better outcomes than those with metastatic disease.

Prevention

Preventive measures include:

• Maintaining a healthy diet rich in fruits, vegetables, and fibre.

• Limiting red and processed meat consumption.

• Smoking cessation.

• Limiting alcohol intake.

• Regular physical activity.

• Weight control.

• Appropriate management of inflammatory bowel disease.

Screening

Because colorectal cancer is often asymptomatic until advanced stages, routine screening is recommended beginning at 50 years of age.

Recommended screening methods include:

• Annual digital rectal examination.

• Annual stool occult blood testing.

• Colonoscopy according to risk category and screening recommendations.

Individuals with hereditary cancer syndromes or strong family history may require earlier screening.