Date post: | 23-Dec-2015 |
Category: |
Documents |
Upload: | posy-barton |
View: | 235 times |
Download: | 0 times |
Bowel Screening in Scotland – Current
Challenges and Possible Solutions
Prof. Bob Steele
Ninewells Hospital, University of Dundee
Proving Screening Works
Population-based randomised trials in which the whole group offered screening (including refusers and interval cancers) is compared with the control group
Disease-Specific Mortality in gFOBT Randomised Trials
(Relative Risks)
• Minnesota– Annual 0.67 (CI 0.51-0.83)– Biennial 0.79 (CI 0.62 - 0.97)
• Nottingham– Biennial 0.85 (CI 0.74 - 0.98)
• Funen– Biennial 0.82 (CI 0.68 - 0.99)
• Göteborg– Biennial 0.84 (CI 0.71-0.99)
National UK Colorectal Cancer Screening Pilot
Aim: to test the feasibility of introducing gFOBT screeing into the NHS
Single Centre
Investigation and treatment devolvedto health boards (n=14)
Age range 50 - 74
Organisation of the bowel cancer screening programme - Scotland
0
1
2
3
4
5
CR
C m
orta
lity/
10
00 p
ers
ons
0 1 2 3 4 5 6 7 8 9 10Years since screening/matched date
Invited for screening Controls
Rate and 95% CI (Nelson-Aalen estimates)Cumulative Mortality from Colorectal Cancer
Rate ratio of Colorectal Cancer invited vs controls
Overall0.90 (0.830 – 0.989)
Relative reduction in CRC mortality 10%
Participants only 0.73 (0.653 – 0.824)
Relative reduction in CRC mortality 27%
Positive Predictive Value of Screening Colonoscopy
CarcinomaCarcinoma
14.6%14.6%
AdenomaAdenoma
35.9%35.9%No NeoplasiaNo Neoplasia
49.5%49.5%
Uptake- Gender and Deprivation
%
SIMD
Round 1 Round 2 Round 3
Screen -detected 351 (56.6%)
208 (46.5%)
139 (35.7%)
True interval 193 (31.2%)
213 (47.7%)
229 (58.9%)
Missed 2 (0.3%)
4 (0.9%)
2 (0.5%)
Miscellaneous 66 (10.7%)
22 (4.9%)
19(4.9%)
Not on Socrates 6(1%)
0 0
Cancers Diagnosed in the Screened Population
Gender distribution - all rounds
%
Site distribution - all rounds
%
Issues to address
• Interval Cancers
• Gender inequality
• Rectal and right-sided cancers
• Uptake
“Blood in stool” tests
Flexible Sigmoidoscopy
Colonoscopy
Colonoscopy
• No RCT results
• Case control studies only
• But – highly sensitive and 100% specific
If an insensitive test with imperfect specificity reduces
mortality…..
Test Accuracy Acceptability Risk
FOBT + +++ -
Flex-sig ++ ++ +
Colonosc +++ + +++£££££
£
ICRF/MRC Study(Oct 1996 – March 1999)
• Single flexible sigmoidoscopy with removal of adenomas– 55-64 years
• High risk colonoscopy– adenoma > 1cm– 3+ adenomas– tubulovillous or villous histology– 20+ hyperplastic polyps above distal rectum– cancer
ICRF/MRC Study
Total no: 354262
Interested : 194726 (55%)
Randomised: 170432
Control: 113178Invited for screening: 57254
Attended: 40674 (71%)
Mortality from CRC
Incidence of CRC
Incidence of L-sided CRC
Incidence of R-sided CRC
Potential Advantages of FS
• Disease prevention– Enhanced detection of left-sided
adenomas
• Detection of rectal cancer
• Unlikely to be a gender difference
Potential Problems with FS
• Uptake– Unlikely to be >30%– Possibility of exaggerated deprivation
gradient
• Effect on right-sided cancers
Alternative Strategy
Increasing sensitivity of FOBT?
gFOBT vs FIT
• gFOBT– Based on Guaiac reaction– Not specific for haemoglobin– Messy to do
• FIT– Immunological– Specific for human haemoglobin– Easy to do– QUANTITATIVE
Normal DD HP LRA HRA Cancer0
100
200
300
400
500
600
700
800
Fae
cal
hae
mo
glo
bin
(n
g/m
l)Quanitative FIT and Disease
n=20358 n=17783
“FIT 400”
n=20358 n=17783
“FIT 50”
Sensitivity Specificity
FIT 50
• 10% positivity rate
• 90% sensitive for cancer• 40% sensitive for adenoma• Lower detection limit may be more sensitive
But…
Question
• Sigmoidoscopy for all
• FIT 50 and colonoscopy for ~ 10%
or ?
Potential Pros
• Sigmoidoscopy– Detection of left-sided adenomas and protection from left sided cancer
– Detection of rectal cancer
• FIT 50– Uptake
– Detection of right-sided cancer