The National Bowel Cancer Screening Program (NBCSP) commenced in 2006, with free faecal occult blood testing (FOBT) targeting the highest incidence ages (50-70) every 5 years, then testing every 2 years at 72 and 74 years (full implementation planned by 2020).
Since implementation, 7% of FOBTs have been positive. Contrary to popular belief, a positive FOBT has a low risk of cancer (~2%) – half have a normal colonoscopy and the rest are mainly simple polyps.
Poor uptake disappointing
The overwhelming disappointment from NBCS is the poor uptake rate (see Table 1) – just 36% (cf. similar English programme ~60%). This is thought to be due to: no direct promotion of the program; low community understanding of bowel cancer risk and the purpose of bowel cancer screening; and some low acceptance of FOBT testing as a screening method amongst primary health care practitioners.
Participation rates increase amongst the older age cohorts most at risk of bowel cancer overall, but is lower in males from lower socioeconomic areas amongst whom there are higher rates of colorectal cancer (CRCa).
There is already evidence NBCSP reduces CRCa mortality in Australia (by 15-33%). Bowel cancer is an ideal disease to screen for: a long premalignant phase (polyps take about 10 years to become cancerous); CRCa survival is strongly stage-dependent (early stage cancers have a high cure rate); and unmeasurable general awareness encourages symptomatic patients to present early.
The ideal screening method is highly debatable: international guidelines differ considerably; and the most recent US guidelines (2016 USPSTF) endorse seven different screening strategies.
Methods of bowel cancer screening
NBCSP uses a 4th generation immunochemical (iFOBT or FIT), which detects antibodies to human haemoglobin. It is more specific than the old guaiac based gFOBT. But both need two or three samples even though the current iFOBT avoids pre-test dietary restriction.
Other faecal and plasma based tests are available (e.g. CEA, circulating tumour DNA) but they are less useful for early stage disease. FIT-DNA may become the FOBT of choice but costs are currently almost as much as a colonoscopy.
Current bowel screening recommendations
Table 2 details current screening recommendations. Almost all patients are in Category 1 (average or slightly increased risk) and hence only need the NBCSP FOBT.
A common clinical issue is screening first degree relatives of a patient with CRCa. This large group (~10% of the population) has a 1 in 7 lifelong risk but colonoscopy is only recommended if the cancer was diagnosed in a young (<55yo) relative; 10 yearly colonoscopy +/- FOBT in-between is a good solution from age 50 (although this is outside guidelines).
The FOBT program selects a high-risk subgroup to undergo colonoscopy. Hence while excellent as a population screening test, it is inaccurate on an individual basis. High quality colonoscopy is essential for screening and requires good prep; the modern split prep administered four to five hours before colonoscopy is best. Completion rates, complication rates and withdrawal times are important. The most widely accepted quality measure is adenoma detection rate (ADR): US data shows significant variation in ADR amongst colonoscopists; and a correlation between ADR and lower risk of developing CRCa.
Colonoscopy is the most commonly performed procedure in WA. However, cost effectiveness is a major issue. The government is formulating new evidence-based codes for colonoscopy e.g. if a patient undergoes a colonoscopy earlier than guidelines recommend for polyp surveillance, this won’t attract a Medicare rebate. While this is commendable from a public health perspective, and we should be scoping more first time patients and doing less follow-ups, patients often do not fit neatly into guideline categories.
Key Messages
- Bowel cancer screening is beneficial and all patients 50-75 years should have it, starting earlier for high risk groups.
- Low uptake of free screening (<40%) in Australia needs improving for which doctors have a large impact – GPs should focus on getting all their 50-75 year olds screened.
- Scope more first time patients and less for follow-up (where colonoscopy is over used).
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