Cancer epidemiology • Epidemiology & public health – understanding and control of disease at population level • The scientific basis – knowledge through probability • Describe problems • Investigate hypotheses • Monitor control
Mar 28, 2015
Cancer epidemiology
• Epidemiology & public health – understanding and control of disease at population level
• The scientific basis – knowledge through probability
• Describe problems
• Investigate hypotheses
• Monitor control
Epidemiology reveals causes
• Time, place and person
• Did exposure cause cancer?
• Was cancer caused by exposure?
Incidence
• New cases
• Not just deaths
• At what age?
• Is it changing?
prevalence
• Current patients – and current cured?
• The ‘patient pathway’
• Including communication and palliative care
• Health services activity = social cost
• Drug treatment – prevalence more valuable than incidence
Why cancer?
• Burden of disease
• Age-related
Cancer 5-year survival in 2004
Mortality 2004
Individual and environment
• Why did I / she get this disease?
• Interaction of organism with exposure
• A probabilistic event …
• Both direct exposure and trigger…
Risk / Probability
• Individual risk - of getting disease
• Population probability – of getting disease
• Attributable risk – for a factor causing disease
• Population attributable risk =
attributable risk x exposures
established risk factors for some cancers: Tobacco smoking (lung, throat, pancreas, stomach, bladder..,
Alcohol (mouth, throat, food pipe, breast, liver) Ultraviolet light (skin)
Lack of exercise (bowel) High fat, low fruit and vegetable diet (bowel)
Obesity (breast, bowel, womb)
The following have not been confirmed or have been disproved: Deodorant
Underwired bras Cuts and bruises
Make-up
Risks and low risks
Epidemiology study designs
• Cohort
• Case-control
Chernobyl
• A cohort study …
Childhood cancers: case-control study
Setting and subjects: Maps of emissions of many different substances were published on the internet by the National Atmospheric Emissions Inventory and
"hotspots" for 2001 were translated to map coordinates. Child cancer addresses were extracted from an earlier inquiry into the
carcinogenic effects of obstetric radiographs; and their postcodes translated to map references.
Main results: Significant birth proximity relative risks were found within 1.0 km of
hotspots for carbon monoxide, PM10 particles, VOCs, nitrogen oxides, benzene, dioxins, 1,3-butadiene, and benz(a)pyrene.
Calculated attributable risks showed that most child cancers and leukaemias are probably initiated by such exposures
Knox EGJournal of Epidemiology and Community Health 2005; 59: 101-105
Epidemiological knowledge
• Non-experimental
• Not truth but probability
• Looking for confounding
Criteria
1. Temporal relationship
• Value of prospective designs
Criteria
2. Plausibility
• Working with biologists
• From animals to humans
Criteria
3. Statistical association
• Note the type of statistics used -
Criteria
4. Dose relationship
• children/adults
• Easy to do in laboratory, difficult to determine in epidemiology
• eg. use distance for chronic exposures
Criteria
5. Specificity
Attributable risklung cancer – 90% from smokingchildhood leukaemia
~ 25% from exhausts, ~ 6% medical radiation <1% from
Necessary but not sufficient potential viral trigger of cancer cell clone
Criteria
6. Consistency / repeatability
• Exposures, populations
• The world as laboratory ….
Canadian Medical Association J. • April 3, 2001; 164 (7)
Integrated oncology - cervical cancer
Control - surveillanceStatistics as vital statistics
Incidence
Survival
• Prognosis for patient and doctor
• Performance of services
Lung & colorectal cancers5- year relative survivalSelected health authorities and England total
Lung Colorectal
% %
Dorset 5.5 56
Oxfordshire 5.2 47
Kensington 8.9 48
Tees 2.8 26
Sunderland 2.6 33
England 5.5 43
5-year relative survival (with 95% CI) for colorectal cancer patients by NHS Trust, London Region,
1996-2001
0
10
20
30
40
50
60
70
NHS Trusts
5-y
ea
r s
urv
iva
l, %
Proportion of patients expressing a problem with each aspect of care
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
London Networks
England average
Not treated with respect and
dignity
Doctor did not discuss the purpose of treatment
In pain or discomfort
Waited too long
Time spent explaining condition
Cancer patient satisfaction
Cancer services in England
Cancer biology - individual and society
• The patient perspective
• The clinical perspective
• The political perspective