Brystkræftscreening og overdiagnostik ‐hvordan forstår vi stigningen i incidens?
Henrik Stø[email protected]
1. December 2016 – Institut for Folkesundhed, AUInstitutseminar, Vingsted
Screening ‐ forskningsområdet• Seniorforskere
• Almen Medicin: Annelli Sandbæk, Peter Vedsted• Epidemiologi: Henrik Møller, Kim Overvad• Sundhedsfremme: Kim Iburg• Biostatistik: Michael Væth, Henrik Støvring• Med flere...
• Valgfag på Kandidatdelen – 10 ECTS• Direkte adgang til at rekruttere studerende fra FSV
• Metodestærke• Kan spottes tidligt på uddannelsen• Fx: Mette Lise Lousdal og Mette Møller
Institut for Folkesundhedsvidenskab og screening• Tværfaglig forskningsgruppe – under opbygning• Screening bør integreres bedre i den epidemiologiske
undervisning• Akut brug for de bedste epidemiologiske metoder• Samfundsrelevant• Fordrer forskellige fagdiscipliner:
• Statistik• Epidemiologi• Sundhedstjenesteforskning• Sundhedsøkonomi• Sundhedskommunikation
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Background: A simple screening model
I
II
III
IV
I
II
IIIIV
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• Definition af lead‐time: ”the length of time diagnosis is advanced by screening”(Biesheuvel et. al. Lancet Oncol 2007)
Background: More complex scenarios
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Aim
Population‐based, open cohort study:
To estimate the effect of introducing a screening program on breast cancer stage distribution • by comparing stage‐specific incidence in women eligible for
screening to the corresponding incidence prior to organized screening
• relative to the concurrent change in younger, ineligible women
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Methods
Population• All Norwegian women of the relevant age in the relevant period• First‐time DCIS or invasive breast cancer (ICD10‐codes: D05 or C50)• Period: 1987‐2011• Birth cohorts: 1917‐1980
Data• Stage, tumor size, and residence at date of diagnosis• Birth year• Survival after diagnosis
• Size of source population
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Relative IRR = IRR eligibleIRR ineligible
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Heuer. Biometrics. 1997
Statistical analysis
Incidence
IRR ineligible
IRR eligible
Results
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Results
Localized stage(I)
Advanced stages(III+IV)
Unadjusted analysis (n=43,489)IRR eligible 2.54 (2.44 to 2.65) 0.80 (0.74 to 0.87)IRR ineligible 1.31 (1.23 to 1.40) 0.80 (0.72 to 0.90)Relative IRR 1.94 (1.79 to 2.09) 1.00 (0.87 to 1.15)
Adjusted for age and calendar timeRelative IRR 1.97 (1.82 to 2.13) 1.04 (0.91 to 1.20)
Adjusted for age, calendar time, and interactionRelative IRR 1.69 (1.52 to 1.89) 1.18 (0.95 to 1.45)
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Results
Localized stage(I)
Advanced stages(III+IV)
Continued follow‐up (n=49,883)Relative IRR 1.68 (1.51 to 1.87) 1.11 (0.90 to 1.36)
Compensatory drop more pronounced for stages I and II than advanced stages
Excluding prevalence rounds (n=38,807)Relative IRR 1.60 (1.42 to 1.79) 1.08 (0.86 to 1.35)
When two youngest cohorts excluded (1.47, 1.30 to 1.66) (1.03, 0.81 to 1.32)
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Manglende fald i avanceret cancer • Mulige forklaringer
• Uobserverbart pga for kort follow‐up• Insensitiv analyse• Uobserveret confounding (kohorte/periodeeffekter)• Der er ikke noget fald
• Kan (til dels) undersøges med en lead time simulationsmodel• Implementeret i Excel• Visualiserer betydningen af
‐ analysestrategi‐ prevalence peak‐ compensatory drop
• Oprindeligt tænkt til brug i undervisning
The screening illustrator
The screening illustrator• The world without screening
The screening illustrator• Moving cases forward in time (lead time!)
The screening illustrator• The world with screening – moved and non‐moved cases
Computing incidence rates (with screening)
Comparing the two worlds
Prevalence peak Compensatory drop
When would we see a drop in advanced cases?• NOTE: Only 20% of advanced cases are moved to another period
Conclusion• No observed change in incidence of advanced breast cancer is
likely because screening cannot prevent advanced cancers• We need better understanding of lead times for mammography
screening• How can we reconcile a finding of reduced mortality with no or
minimal prevention of advanced stage breast cancer?
• Screening poses complex epidemiology questions• An important public health topic• A core component in any education in public health
Thanks for your attention – questions welcome!
(Aarhus University, March 2016 – H Støvring)
