Bowel Cancer Screening
The NHS Bowel Cancer Screening Programme uses the faecal immunochemical test to detect occult blood in stool, enabling early detection of colorectal cancer and adenomatous polyps in asymptomatic adults.
Key Facts
NHS Bowel Cancer Screening uses FIT (faecal immunochemical test) sent by post every 2 years to adults aged 50-74 in England (age range expanding from 60-74) FIT detects human haemoglobin in stool; threshold ≥120 mcg Hb/g faeces triggers referral for colonoscopy Colorectal cancer is the 4th most common cancer in the UK: approximately 42,000 new cases/year and 16,000 deaths/year Screening reduces colorectal cancer mortality by approximately 16-25% in screened populations FIT-positive rate: approximately 2-3% of those screened; of those, 10% have cancer and 40% have adenomas on colonoscopy Bowel scope screening (one-off flexible sigmoidoscopy at age 55) is being phased out in favour of FIT Lynch syndrome and familial adenomatous polyposis patients require separate surveillance colonoscopy programmes GP role: encourage uptake, manage results, refer symptomatic patients via 2-week-wait pathway regardless of screening
Overview
Key Facts
Colorectal cancer is a leading cause of cancer death in the UK. Screening enables detection at an earlier, more treatable stage and identification of pre-malignant adenomatous polyps. FIT is the current standard screening test.
Epidemiology
- Colorectal cancer: 4th most common cancer in UK; 2nd most common cause of cancer death
- Approximately 42,000 new cases and 16,000 deaths annually
- Lifetime risk: approximately 1 in 15 for men; 1 in 18 for women
- 90% of colorectal cancers occur in people aged >50
- Stage at diagnosis significantly affects prognosis: stage I 5-year survival >90%; stage IV <10%
Programme Structure
- FIT: every 2 years for adults aged 50-74 (phased expansion from previous 60-74 age range)
- Postal kit: single stool sample; specific for human haemoglobin
- Threshold: ≥120 mcg Hb/g faeces → colonoscopy referral
- One-off flexible sigmoidoscopy at age 55 (bowel scope) being phased out
Pathology
- Most colorectal cancers arise through the adenoma-carcinoma sequence (Vogelstein model) over 10-15 years
- Key mutations: APC → KRAS → TP53 → invasive carcinoma
- Adenomatous polyps: tubular, tubulovillous, villous (increasing malignant potential)
- Serrated pathway: sessile serrated lesions → microsatellite-unstable cancers (15-20% of CRC)
Clinical Presentation
Screening Context (Asymptomatic)
- FIT-positive patients are asymptomatic; colonoscopy investigates for cancer or adenomas
- Important to distinguish screening pathway from symptomatic pathway
Symptomatic Presentation (Refer — Do NOT Await Screening)
- Change in bowel habit (especially >60 years)
- Rectal bleeding
- Iron deficiency anaemia
- Abdominal mass
- Weight loss
Red Flags (NICE NG12 — 2-Week-Wait Referral)
- Age ≥40 with unexplained weight loss AND abdominal pain
- Age ≥50 with unexplained rectal bleeding
- Age ≥60 with iron deficiency anaemia OR change in bowel habit
- Rectal or abdominal mass
- FIT ≥10 mcg Hb/g in symptomatic patients (NICE DG30)
Differential Diagnosis
| FIT Positive — Colonoscopy Finding | Frequency | Action |
|---|---|---|
| Normal | ~50% | Reassurance, return to screening |
| Adenomatous polyps | ~40% | Polypectomy, surveillance programme |
| Colorectal cancer | ~10% | MDT discussion, staging, treatment |
| Inflammatory bowel disease | Uncommon | Appropriate referral |
| Diverticular disease | Common incidental finding | Manage if symptomatic |
| Angiodysplasia | Uncommon | Endoscopic treatment if bleeding |
Diagnosis / Investigation
Screening Test
- FIT: quantitative; measures haemoglobin concentration in stool
- More sensitive and specific than previous guaiac FOBt
- Single sample required (improved uptake vs old 3-sample test)
- Sensitivity for CRC: approximately 80-90% at ≥120 threshold
Colonoscopy (following positive FIT)
- Gold standard investigation for colorectal assessment
- Allows biopsy and polypectomy at same procedure
- Preparation: bowel prep (e.g. Moviprep)
- Complications: perforation risk 1 in 1,000; bleeding after polypectomy 1 in 100
Additional Investigations for Diagnosed CRC
- CT chest/abdomen/pelvis: staging
- MRI pelvis: for rectal cancer staging
- CEA: tumour marker (baseline and monitoring)
- Mismatch repair/microsatellite instability testing: for all CRC (Lynch syndrome screening)
FIT in Symptomatic Patients (NICE DG30)
- FIT ≥10 mcg Hb/g: refer via 2-week-wait pathway
- Used for symptomatic patients who do not meet 2-week-wait criteria based on symptoms alone
Management
Primary Care Role
- Encourage screening uptake (address barriers: embarrassment, fear, language, access)
- Ensure patients understand how to use FIT kit
- Manage results: positive FIT → explain colonoscopy referral; negative FIT → routine recall
- Support patients through diagnostic pathway
- Symptomatic patients: refer independently of screening via 2-week-wait if criteria met
Polyp Management
- Endoscopic polypectomy at colonoscopy
- Histological assessment determines surveillance schedule
- Low risk (1-2 adenomas, all <10mm, no HGD): no surveillance; return to screening
- Intermediate risk (3-4 small adenomas, OR ≥1 adenoma ≥10mm): surveillance colonoscopy at 3 years
- High risk (≥5 adenomas, OR ≥3 with ≥1 ≥10mm): surveillance at 1 year
Colorectal Cancer Treatment (Specialist-Led)
- MDT discussion for all cases
- Surgery: right/left hemicolectomy, anterior resection, abdominoperineal resection
- Chemotherapy: adjuvant FOLFOX (5-FU, oxaliplatin, folinic acid) for stage III; palliative for stage IV
- Radiotherapy: neoadjuvant for rectal cancer
- Targeted therapy: cetuximab, bevacizumab for metastatic disease
- Immunotherapy: pembrolizumab for MSI-high/dMMR metastatic CRC
Referral Criteria
- FIT positive: colonoscopy via screening programme
- Symptomatic meeting NICE NG12 criteria: 2-week-wait referral
- Family history of CRC/Lynch syndrome: genetics referral and surveillance colonoscopy
Prognosis
- Screen-detected CRC: majority diagnosed at stage I-II; 5-year survival >80%
- Symptomatic CRC: often diagnosed at later stage; overall 5-year survival 55-60%
- Stage-specific survival: stage I >90%, stage II 80%, stage III 65%, stage IV <10%
- Screening reduces CRC mortality by approximately 16-25%
- Adenoma detection and removal prevents an estimated 30% of future CRC
- Lynch syndrome carriers: lifetime CRC risk 40-80% without surveillance; significantly reduced with regular colonoscopy
Other Relevant Information
Colorectal Cancer Staging (Dukes/TNM)
| Dukes | TNM | Description | 5-year Survival |
|---|---|---|---|
| A | T1-2, N0, M0 | Confined to bowel wall | >90% |
| B | T3-4, N0, M0 | Through bowel wall | 75-80% |
| C | Any T, N1-2, M0 | Lymph node involvement | 60-65% |
| D | Any T, Any N, M1 | Distant metastases | <10% |
BSG Polyp Surveillance Guidelines
| Risk | Criteria | Surveillance |
|---|---|---|
| Low | 1-2 adenomas <10mm, no HGD | Return to screening |
| Intermediate | 3-4 small OR ≥1 ≥10mm | Colonoscopy at 3 years |
| High | ≥5 adenomas OR ≥3 with ≥1 ≥10mm | Colonoscopy at 1 year |