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
Risks and low risks 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
Epidemiology study designs • Cohort • Case-control
Chernobyl • A cohort study …
Childhood cancers: case-control study Knox EG Journal of Epidemiology and Community Health 2005; 59: 101-105 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
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 • Specificity Attributable risk lung cancer – 90% from smoking childhood 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 ….
Integrated oncology - cervical cancer Canadian Medical Association J. • April 3, 2001; 164 (7)
Control - surveillance Statistics as vital statistics
Prognosis for patient and doctor Performance of services Survival
Lung & colorectal cancers 5- year relative survival Selected health authorities and England total
Cancer biology - individual and society • The patient perspective • The clinical perspective • The political perspective