Report in English with a Dutch summary (KCE reports 45A)

120 Screening for Colorectal Cancer KCE reports vol.45
Sensitivity analysis
Rather surprisingly, Wong did not perform sensitivity analysis on his cost
effectiveness outcomes and Ladabaum only performed such an analysis on the
demand for health services. Three studies did not perform sensitivity analysis
with respect to FOBT or colonoscopy compared to no screening. The Israeli
study only performed sensitivity analysis on the ICER of colonoscopy compared
with FOBT+SIG, the Taiwanese study identified the influential parameters on
the ICER for stool DNA testing compared with no screening, and Frazier
performed the analysis on the ICER of rehydrated FOBT with 5-yearly
sigmoidoscopy versus no screening.
O Leary performed a sensitivity analysis on costs. The cost of the screening
program was an important determinant of the cost-effectiveness of FOBT. The
ICER of biennial FOBT screening was increased slightly from 24.710
(AUD41.183) to 29.295 (AUD48.824) if administrative costs for the screening
program increased from 45 (AUD75) to 60 (AUD100) but decreased
dramatically to 9455 (AUD15.758) if these costs were omitted. With respect
to discounting there were no surprising results, i.e. outcomes were better when
not discounting the benefits, the opposite happened for costs, and there was a
relatively larger influence on the ICER of discounting benefits compared to
costs.
Only two studies performed sensitivity analysis changing screening intervals.
O Leary already compared annual and biennial FOBT screening in their base
analysis, which provided better cost effectiveness outcomes for the 2-yearly
screening schedule. Sonnenberg changed both the frequency of FOBT and
colonoscopy. If the frequency of colonoscopy is increased to once every 5
years, the incremental cost-effectiveness of colonoscopy compared with FOBT
increases from a baseline value of about 8990 ($11.382) to 21.750 ($27.529).
In combination with a lower efficacy (50% instead of 75%) and an 80%
compliance (instead of 100%) the ICER would even increase to about 43.100
($54.561). Shortening the interval of repeated colonoscopy also affects the
ICER of FOBT which increases from 7670 ($9705) to 16.390 ($20.746).
Reducing the frequency of screening with FOBT from once annually to once
every 3 years slightly increased the ICER form 7670 ($9705) to 7775
($9843), as costs savings became partly negated by fewer life-years saved
through early cancer detection (Sonnenberg).
Furthermore, according to Sonnenberg, FOBT is particularly sensitive to
changes in the compliance rate of repeated testing because it is done more
frequently than colonoscopy. For instance, a decrease of compliance with annual
test repetition to 90% (base case 100%) increases the ICER of FOBT to about
11.680 ($14.788) (base case 7670 ($9705)). Low compliance with
colonoscopy after a positive result on FOBT also renders the initial screening
technique less efficacious and increases its associated costs per saved life-year. If
only 75% (base case 100%) of positive FOBTs were followed by colonoscopy,
the incremental cost-effectiveness ratio of FOBT would increase to 8120
($10.281). Also in the study of O Leary, ICERs improved if compliance
increased. Finally, Maciosek found that adherence was less influential on results
than gains in life expectancy and net costs. However, exact outcomes were not
presented.
Sonnenberg also analysed the influence of changing test characteristics.
Improvement of test sensitivity results in detection of cancers at an earlier stage
and reduced mortality from colorectal cancer. Improved specificity results in