Bowel cancer screening
Screening vs surveillance
- Population screening (asymptomatic, average risk) vs surveillance (past neoplasia, IBD, family history) - different programs, different intervals
National Bowel Cancer Screening Program (NBCSP)
- iFOBT posted to everyone aged 50-74, 2-yearly
- Eligible age lowered to 45 from 1 July 2024
- 45-49 must REQUEST the first kit (then enter the routine 2-yearly mailout); 50-74 are sent it automatically
- Immunochemical FOBT - specific for human globin
- No dietary or drug restriction needed (unlike the old guaiac test)
- Positive iFOBT -> colonoscopy, target within 30 days
Epidemiology
- CRC: ~2nd commonest cause of cancer death in Australia; ~15,000 new cases/yr
- Lifetime risk ~1 in 20
- Incidence rising in adults <50 - the reason the screening age was lowered
- NBCSP participation only ~40-45%; ~4-5% of kits are positive
- Screening-detected cancers are earlier stage -> iFOBT screening reduces CRC mortality by ~15-25%
Why screening works - the adenoma-carcinoma sequence
- Adenoma-carcinoma sequence - APC -> KRAS -> TP53; ~10 years from adenoma to cancer
- That long dwell time is what makes interval screening work
- Serrated pathway - BRAF, CpG island methylation, MSI; sessile serrated lesions, right-sided, flat, easily missed
- Lynch (MMR deficiency) - accelerated sequence, interval cancers within 2-3 years -> shorter intervals
- Adenomas bleed intermittently -> a single negative iFOBT never excludes neoplasia; repetition is the point
GESA/NHMRC risk categories - set by family history
GESA/NHMRC risk categories - set by family history
| Category | Definition |
|---|---|
| Average / slightly increased | Everyone else, including ONE first-degree relative diagnosed >=55 (~2x average - still not enough to change the pathway) |
| Moderately increased | One FDR diagnosed <55, OR two FDR/SDR on the same side at any age |
| High | One FDR plus >=2 first/second-degree relatives on the same side; or fewer relatives where there are multiple CRCs in one person, CRC <50, or other Lynch-spectrum cancers; OR a known autosomal dominant syndrome (Lynch, FAP); OR a sibling of a MUTYH-associated polyposis patient |
- Lynch-spectrum cancers: endometrial, ovarian, gastric, small bowel, urothelial, hepatobiliary, brain, sebaceous
- Screening is for the asymptomatic
- *Symptoms (rectal bleeding, iron deficiency, altered bowel habit, weight loss) = diagnostic colonoscopy, not an iFOBT*
- A negative iFOBT in a symptomatic patient is dangerously falsely reassuring
Average / slightly increased risk
A. Average / slightly increased risk
- iFOBT 2-yearly, age 45-74 (NBCSP)
- Aspirin - consider low-dose for CRC chemoprevention age 50-70, discuss bleeding risk
Moderately increased risk (family history)
B. Moderately increased risk (family history)
- Colonoscopy 5-yearly from age 50, OR 10 years before the youngest affected relative's diagnosis, whichever is earlier
- iFOBT 2-yearly in the intervening years
High risk
C. High risk
- Referral for genetic assessment
- Lynch: colonoscopy 1-2 yearly from 25 (or 5 yr before earliest family diagnosis); consider aspirin (CAPP2); gynaecological surveillance
- FAP: annual sigmoidoscopy/colonoscopy from 12-15, then prophylactic colectomy; upper endoscopy for duodenal adenomas
- MUTYH-associated polyposis: colonoscopy 1-2 yearly from 18-20 in biallelic carriers
Post-polypectomy surveillance
D. Post-polypectomy surveillance
| Findings | Next colonoscopy |
|---|---|
| <3 polyps, ALL "simple" (<10 mm, no high-grade dysplasia, no villous component) | 5 years |
| >=3 polyps, OR any "advanced" polyp (>=10 mm, high-grade dysplasia, or villous) | 3 years |
- Interval resets on the findings of each subsequent colonoscopy
- Piecemeal EMR of a large lesion -> site check at 3-6 months, separate from the interval above
IBD colitis surveillance
E. IBD colitis surveillance
- Start 8 years after diagnosis of pancolitis; 12-15 years for left-sided colitis; from the time of diagnosis if PSC
| Frequency | When |
|---|---|
| Yearly | Active inflammation, PSC, FDR with CRC <50, stricture / short colon / multiple pseudopolyps |
| 3-yearly | Inactive disease without those factors |
| 5-yearly | Last two colonoscopies macroscopically AND histologically normal |
- Chromoendoscopy or high-definition white light with targeted biopsies
- *Proctitis alone does not carry increased risk* - no surveillance needed
- 5-ASA and thiopurines are associated with reduced CRC risk
Stop screening
- >75, or when comorbidity means a cancer found would not be treated - the harms of colonoscopy overtake the benefit
Risk modifiers and syndromes
- IBD - risk rises with duration, extent and severity of inflammation; equal in UC and Crohn colitis for equivalent extent
- PSC - the single strongest IBD modifier; surveillance from diagnosis, lifelong
- Lynch syndrome, FAP, MUTYH-associated polyposis, Peutz-Jeghers, juvenile polyposis, serrated polyposis syndrome
- Acromegaly, ureterosigmoidostomy, prior abdominal/pelvic radiotherapy, renal transplant
- **Streptococcus gallolyticus (bovis) bacteraemia or endocarditis -> colonoscopy**
- Obesity, T2DM, smoking, processed/red meat, alcohol, sedentary
Colonoscopy quality
- Colonoscopy quality determines outcome
- Adenoma detection rate >=25-30% and caecal intubation >=90% are the key indicators
- Every 1% rise in ADR -> ~3% fall in interval cancer
- Interval cancers ~3-8% of CRC after colonoscopy - missed lesions, incomplete resection, flat serrated lesions, Lynch
- Colonoscopy complications: perforation ~1 in 1000, bleeding ~1 in 300 after polypectomy - quote these when consenting
- Stage at diagnosis drives survival: 5-yr ~90% stage I vs ~13% stage IV - the entire rationale for screening
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