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