Summary

Colorectal cancer (CRC) is the third most common cancer worldwide and the second leading cause of cancer death. It arises from the epithelium of the colon or rectum, typically through the adenoma-carcinoma sequence. Approximately 90% are adenocarcinomas. Risk factors include age, family history, inflammatory bowel disease, and lifestyle factors (diet, obesity, smoking, alcohol). Population screening with the faecal immunochemical test (FIT) has been shown to reduce mortality. Diagnosis requires colonoscopy with biopsy, and staging involves CT chest-abdomen-pelvis and MRI pelvis for rectal tumours. Treatment is stage-dependent: early tumours may be cured with surgery alone, while locally advanced and metastatic disease require multimodal therapy including chemotherapy and radiotherapy.

Key Facts

• Prevalence: 3rd most common cancer; ~42,000 new cases/year in UK
• Mortality: 2nd leading cause of cancer death
• Adenoma-carcinoma sequence: 90% arise from adenomatous polyps (Vogelstein model)
• Screening (UK): FIT test every 2 years, ages 50-74 (lowered from 60)
• Left-sided: More likely to obstruct (narrower lumen)
• Right-sided: Often presents late (anaemia, mass); occult bleeding
• Rectal cancer: Requires MRI for local staging; neoadjuvant chemoradiotherapy for T3/T4/N+
• Staging: Dukes' (historical) vs TNM; determines prognosis and treatment
• Adjuvant chemotherapy: Standard for Stage III (node-positive); FOLFOX
• 5-year survival: Stage I: 90%; Stage IV: ~10-15%

Clinical Pearls

"Right = Silent, Left = Symptomatic": Right-sided colon cancers (caecum, ascending colon) often present late with iron deficiency anaemia and a palpable mass. Left-sided cancers (descending, sigmoid) cause obstruction and change in bowel habit earlier due to narrower lumen.

"FIT Is the Gatekeeper": The Faecal Immunochemical Test (FIT) detects haemoglobin in stool. A positive FIT warrants colonoscopy. The NHS bowel screening programme saves lives through early detection.

"Rectal = MRI First, Then MDT": Rectal cancer requires MRI pelvis for accurate local staging (T stage, CRM involvement, EMVI) to plan neoadjuvant therapy and surgical approach.

"Lynch Syndrome: MSI-H = Better Prognosis": Microsatellite instability-high (MSI-H) tumours (Lynch syndrome, sporadic MSI-H) have better prognosis and respond to immunotherapy.

"TME Is Gold Standard for Rectal": Total Mesorectal Excision (TME) is the standard surgical technique for rectal cancer — excises rectum with surrounding mesorectum en bloc, reducing local recurrence.

Why This Matters Clinically

Colorectal cancer is common, preventable, and curable if detected early. Every clinician should recognise red flag symptoms (change in bowel habit, iron deficiency anaemia, rectal bleeding), understand the screening programme, and know when to refer urgently under the 2-week wait pathway.[1,2]

Approach

General:

• Cachexia, pallor (anaemia)
• Lymphadenopathy (Virchow's node — left supraclavicular)

Abdominal Examination:

• Inspection: Distension (obstruction)
• Palpation: Mass (RIF, RLQ, LIF), hepatomegaly
• Percussion: Ascites (carcinomatosis)
• Auscultation: High-pitched bowel sounds (obstruction)

Digital Rectal Examination (DRE):

• Essential for rectal cancer
• Assess mass: Position, mobility, size
• Fixed mass = T4 / advanced
• Mucus or blood on examining finger

Survival by Stage

Prognostic Factors

Key Guidelines

Landmark Trials

MOSAIC Trial (2004)

• Adjuvant FOLFOX vs 5-FU/LV for Stage II/III colon cancer
• FOLFOX improved 5-year DFS by 6.4%
• Established FOLFOX as standard adjuvant therapy
• PMID: 15175435

KEYNOTE-177 (2020)

• Pembrolizumab vs chemotherapy for MSI-H/dMMR metastatic CRC
• Pembrolizumab improved PFS significantly
• Changed practice for MSI-H tumours
• PMID: 33264544

What is Bowel Cancer?

Bowel cancer (colorectal cancer) is cancer that starts in the large bowel (colon) or back passage (rectum). It usually develops slowly from growths called polyps.

Who is at risk?

• Age over 50 (most cases)
• Family history of bowel cancer
• Diet high in red or processed meat
• Being overweight
• Smoking and alcohol

What are the symptoms?

• Change in bowel habit (looser stools, more frequent)
• Blood in your poo
• Unexplained weight loss
• Tiredness (from anaemia)
• A lump in your tummy

How is it detected early?

The NHS Bowel Screening Programme sends home testing kits (FIT) to everyone aged 50-74. If positive, you'll have a colonoscopy.

How is it treated?

• Surgery: Removing the affected part of the bowel
• Chemotherapy: After surgery if the cancer has spread to lymph nodes
• Radiotherapy: Often before surgery for rectal cancer
• Targeted therapy: For advanced cases

What's the outlook?

If caught early, bowel cancer is very curable. That's why screening is so important.

High-Yield Exam Topics

Sample Viva Questions

Q1: A 60-year-old presents with iron deficiency anaemia. How do you investigate?

Model Answer: Iron deficiency anaemia in an adult is GI malignancy until proven otherwise. I would confirm iron deficiency (low ferritin, low MCV, low serum iron, high TIBC). Upper AND lower GI investigation is required. I would arrange colonoscopy (to exclude colorectal cancer) and OGD (to exclude gastric cancer, coeliac disease). If colonoscopy is incomplete, CT colonography can assess the proximal colon. Blood on examination warrants urgent referral — IDA in the presence of rectal bleeding should trigger 2-week wait referral.

Q2: Describe the staging investigations for rectal cancer.

Model Answer: Rectal cancer staging requires both local and distant assessment:

• CT CAP: For distant metastases (liver, lung, nodes)
• MRI Pelvis: Gold standard for local staging; assesses T stage (depth of invasion), circumferential resection margin (CRM) involvement, extramural venous invasion (EMVI), relationship to pelvic structures
• The CRM on MRI predicts risk of local recurrence. Threatened CRM (<1mm) typically requires neoadjuvant chemoradiotherapy.
• TNM staging determined by imaging guides MDT decision for neoadjuvant therapy vs primary surgery.

Q3: When is adjuvant chemotherapy indicated for colon cancer?

Model Answer: Adjuvant chemotherapy is indicated for:

• Stage III (node-positive): Standard of care; FOLFOX or CAPOX for 3-6 months (IDEA trial supports 3 months for lower-risk Stage III)
• High-risk Stage II: Consider if negative prognostic features (T4, <12 nodes harvested, perforation, lymphovascular invasion, poorly differentiated histology)
• Stage I: No adjuvant chemotherapy (surgery alone is curative)
• Stage IV: Adjuvant chemotherapy is not applicable; treated with palliative/systemic chemotherapy

Common Exam Errors

Last Reviewed: 2025-12-24 | MedVellum Editorial Team

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.