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Bowel Screening in Scotland – Current Challenges and Possible Solutions Prof. Bob Steele Ninewells Hospital, University of Dundee
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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
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Disease-Specific Mortality in gFOBT Randomised Trials (Relative Risks) Minnesota –Annual0.67 (CI 0.51-0.83) –Biennial0.79 (CI 0.62 - 0.97) Nottingham –Biennial0.85 (CI 0.74 - 0.98) Funen –Biennial0.82 (CI 0.68 - 0.99) Göteborg –Biennial0.84 (CI 0.71-0.99)
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National UK Colorectal Cancer Screening Pilot Aim: to test the feasibility of introducing gFOBT screeing into the NHS
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Single Centre Investigation and treatment devolved to health boards (n=14) Age range 50 - 74 Organisation of the bowel cancer screening programme - Scotland
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Rate ratio of Colorectal Cancer invited vs controls Overall 0.90 (0.830 – 0.989) Relative reduction in CRC mortality 10% Participants only 0.73 (0.653 – 0.824) Relative reduction in CRC mortality 27%
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Positive Predictive Value of Screening Colonoscopy Carcinoma14.6% Adenoma35.9% No Neoplasia 49.5%
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Uptake - Gender and Deprivation % SIMD
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Round 1Round 2Round 3 Screen -detected351 (56.6%) 208 (46.5%) 139 (35.7%) True interval193 (31.2%) 213 (47.7%) 229 (58.9%) Missed2 (0.3%) 4 (0.9%) 2 (0.5%) Miscellaneous66 (10.7%) 22 (4.9%) 19 (4.9%) Not on Socrates6 (1%) 00 Cancers Diagnosed in the Screened Population
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Gender distribution - all rounds %
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Site distribution - all rounds %
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Issues to address Interval Cancers Gender inequality Rectal and right-sided cancers Uptake
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“Blood in stool” tests Flexible Sigmoidoscopy Colonoscopy
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No RCT results Case control studies only But – highly sensitive and 100% specific
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If an insensitive test with imperfect specificity reduces mortality…..
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TestAccuracyAcceptabilityRisk FOBT++++- Flex-sig++ + Colonosc++++ £££££ £
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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
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ICRF/MRC Study Total no: 354262 Interested : 194726 (55%) Randomised: 170432 Control: 113178 Invited for screening: 57254 Attended: 40674 (71%)
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Mortality from CRC
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Incidence of CRC
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Incidence of L-sided CRC
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Incidence of R-sided CRC
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Potential Advantages of FS Disease prevention –Enhanced detection of left-sided adenomas Detection of rectal cancer Unlikely to be a gender difference
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Potential Problems with FS Uptake –Unlikely to be >30% –Possibility of exaggerated deprivation gradient Effect on right-sided cancers
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Alternative Strategy Increasing sensitivity of FOBT?
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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
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Quanitative FIT and Disease
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n=20358 n=17783 “FIT 400”
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n=20358 n=17783 “FIT 50”
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Sensitivity Specificity
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FIT 50 10% positivity rate 90% sensitive for cancer 40% sensitive for adenoma Lower detection limit may be more sensitive But…
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Question Sigmoidoscopy for all FIT 50 and colonoscopy for ~ 10% or ?
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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
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