About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Third most common cancer in the UK (~42,000 new cases/year). Lifetime risk ~1 in 15
- Most arise via adenoma → carcinoma sequence (APC → KRAS → p53 mutations). Takes ~10 years
- Screening: NHS bowel cancer screening programme — FIT sent to everyone aged 54–74 every 2 years
- Suspected cancer referral: FIT ≥10 µg Hb/g faeces → 2-week-wait referral (NICE NG12/DG56)
- Curative treatment: surgical resection (right hemicolectomy, left hemicolectomy, anterior resection, APR) ± adjuvant chemotherapy
Overview
Colorectal cancer (CRC) is the fourth most common cancer in the UK. The majority (>95%) are adenocarcinomas arising from pre-existing adenomatous polyps via the well-characterised adenoma-carcinoma sequence involving sequential genetic mutations (APC, KRAS, SMAD4, TP53). Risk factors include age >50, family history, inflammatory bowel disease (especially UC with pancolitis), Lynch syndrome (HNPCC), familial adenomatous polyposis (FAP), obesity, processed meat, alcohol, and smoking. Left-sided tumours tend to present with altered bowel habit and rectal bleeding; right-sided tumours often present later with iron deficiency anaemia.
Epidemiology
Approximately 42,000 new cases per year in the UK, making it the fourth most common cancer and second most common cause of cancer death. Lifetime risk is approximately 1 in 15. Incidence rises sharply after age 50 and peaks in the 80s. Five-year survival is approximately 60% overall but ranges from >90% (Dukes A/stage I) to <10% (Dukes D/stage IV). The NHS bowel cancer screening programme (FIT-based) has improved early detection since its introduction.
Clinical Features
Symptoms
Change in bowel habit (especially >4 weeks, looser/more frequent stools)
Rectal bleeding (dark red mixed with stool — left-sided tumours)
Iron deficiency anaemia (often the only presentation of right-sided tumours)
Unexplained weight loss
Abdominal pain (especially colicky — may indicate partial obstruction)
Tenesmus (sensation of incomplete evacuation — rectal tumours)
Mucus per rectum
Large bowel obstruction as emergency presentation (~20%)
Signs
Palpable abdominal mass (right-sided tumours)
Palpable rectal mass on DRE (rectal tumours — ~60% are within reach)
Pallor (iron deficiency anaemia)
Hepatomegaly (liver metastases)
Abdominal distension (obstruction)
Cachexia (advanced disease)
Investigations
First-line
FIT (faecal immunochemical test)Quantitative FIT ≥10 µg Hb/g faeces → 2WW referral for suspected colorectal cancer. Replacing guaiac FOBt in screening and primary care
FBCIron deficiency anaemia (low MCV, low ferritin) — always investigate in men and postmenopausal women
Digital rectal examinationEssential — up to 60% of rectal tumours palpable on DRE
Second-line
ColonoscopyGold standard investigation — visualises entire colon, allows biopsy and polypectomy. Sensitivity >95% for CRC
CT colonography (virtual colonoscopy)Alternative if colonoscopy incomplete, contraindicated, or patient preference
CEA (carcinoembryonic antigen)Baseline for monitoring post-treatment (NOT a screening test). Used to detect recurrence
Specialist
CT chest/abdomen/pelvis (staging CT)Assess for metastatic disease — liver (most common metastatic site), lung, peritoneum
MRI pelvisFor rectal cancer — assess T-stage (depth of invasion), circumferential resection margin, lymph node involvement, and relationship to mesorectal fascia
PET-CTIf liver or lung metastases being considered for surgical resection — assess operability
Microsatellite instability (MSI)/mismatch repair (MMR) testingAll CRC tumours should be tested — identifies Lynch syndrome and guides immunotherapy eligibility
Management
NICE NG151 (Colorectal cancer), 20201
Surgical resection (curative intent)
- Right hemicolectomy: caecal and ascending colon tumours
- Left hemicolectomy: descending colon tumours
- Sigmoid colectomy: sigmoid tumours
- Anterior resection: upper rectal tumours (sphincter-preserving)
- Abdominoperineal resection (APR): low rectal tumours — permanent stoma
- Laparoscopic approach preferred where appropriate
- Total mesorectal excision (TME) for rectal cancer
2
Adjuvant chemotherapy
- Stage III (node-positive): adjuvant chemotherapy with capecitabine ± oxaliplatin (CAPOX) for 3–6 months
- Stage II with high-risk features: consider adjuvant chemotherapy (T4, perforation, poorly differentiated, lymphovascular invasion)
- Stage I: surgery alone, no adjuvant therapy needed
3
Rectal cancer — neoadjuvant
- Neoadjuvant chemoradiotherapy (CRT): for locally advanced rectal cancer (T3/T4 or node-positive on MRI)
- Aims to downstage tumour, improve resection margins, and reduce local recurrence
- Short-course radiotherapy (5 × 5 Gy) for less advanced rectal tumours
4
Metastatic disease
- Liver metastases: surgical resection if resectable (5-year survival ~40% post-resection)
- Systemic chemotherapy: FOLFOX, FOLFIRI, capecitabine + biologics (cetuximab if RAS wild-type, bevacizumab)
- Immunotherapy: pembrolizumab for MSI-high/dMMR metastatic CRC (first-line)
- Palliative stenting for obstructing tumours
- Best supportive care discussion for advanced non-resectable disease
5
Surveillance post-curative treatment
- CEA: every 6 months for 3 years, then annually for 2 years
- CT chest/abdomen/pelvis: at 1 and 3 years minimum
- Surveillance colonoscopy: at 1 year, then every 3 years (to detect metachronous polyps/cancers)
Complications
- Bowel obstruction: ~20% present as emergency with large bowel obstruction
- Perforation: Tumour or proximal to obstruction (caecal perforation)
- Liver metastases: Present in ~25% at diagnosis — most common site of distant spread
- Anastomotic leak: Post-surgical complication — sepsis, peritonitis
- Iron deficiency anaemia: Chronic occult blood loss — may be the only presentation of right-sided CRC
UKMLA Exam Tips
- 1RIGHT-sided CRC: iron deficiency anaemia, abdominal mass, late presentation. LEFT-sided: rectal bleeding, change in bowel habit
- 2FIT ≥10 µg Hb/g → 2WW referral. Rectal mass on DRE → 2WW referral WITHOUT FIT
- 3Adenoma-carcinoma sequence: APC (gatekeeper) → KRAS → SMAD4 → p53 → carcinoma (~10-year process)
- 4Lynch syndrome (HNPCC): autosomal dominant, DNA mismatch repair gene mutations (MLH1, MSH2, MSH6, PMS2). Test ALL CRC tumours for MSI/MMR
- 5CEA is a MONITORING marker, NOT a screening test — used to detect recurrence post-surgery
- 6Duke's staging (still commonly examined): A = confined to bowel wall, B = through wall, C = lymph nodes, D = distant metastases
- 7NHS bowel screening: FIT sent every 2 years to everyone aged 54–74 (expanding to 50–74)
practicetest your knowledge on colorectal cancerApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — gastroenterology and beyond.
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