Lecture 2 - Cancer and Environmental Factors Flashcards
What did a study looking at a cancer risk by country find/
Lots of variation between countries in total cancer risk and risk of individual cancers
Thought to be due to differences in culture, lifestyle and environmental factors
What proportion of cancer deaths are attributed to non-genetic factors. What are the two most common non-genetic causes of cancer?
75%
tobacco and diet
What did the study looking at japanese populations and migrating to hawaii show?
- levels of certain cancer risk changed dramatically postmigration, though genetics hadn’t changed
- shows that environment has a significant effect on incidence
What did Pott notice in chimney sweeps?
correlation between soot lodging in the folds of scrotal skin and skin cancer of the scrootum
How are carcinogens classified, using the current IARC system?
- definite carcinogen = an association has been established and chance, bias and cofounding can be ruled out with reasonable confidence
- probable carcinogen = association has been established but chance, bias and confounding cannot be ruled out with reasonable confidence
- possible carcinogen = available studies are of insufficient quality, consistency or statistical power to permit a conclusion of probable association
What are the 3 aspects of risk assessment?
potency = potential to cause cancer with a particular dose
type of exposure = acute or chronic, avoidable or unavoidable
dose response = cancer risk with different exposures
What can be included in the concept of environmental health affecting human health?
diet, lifestyle, infectious disease
outdoor and indoor air pollution, soil and drinking water contaminants
What makes up outdoor air pollution?
What are the sources of air pollution?
particulate matter nitrogen/sulphur dioxide ozone gas CO polycyclic aromatic hydrocarbons (PAHs) SOURCES= transport, industry, farming, cooking/heating, natural pollutants
elevated urban/rural ratios with many cancer, such as…
mouth and throat nasopharunx oesophagus stomach colon breast bladder prostate
Describe ‘linking nicotine addiction and lung cancer through tobacco-smoke carcinogens’
Nicotine –> tobacco carcinogen exposure by addiction –> DNA adducts –> mutations –> lung cancer
What does the dose-exposure graph look like for smoking and chronic lung disease, lung cancer, CHD and CVD
linear correlation
What is the direct and indirect effect of diet on cancer risk
direct = particular components added to the diet that are responsible to increased or decreased risk indirect = effect involving the balance of the diet
What foods are probable carcinogens? Who was this announced by? What was their evidence?
processed and red meats
WHO
800 epidemiological studies
What are examples of food that fight cancer?
fibre (NSP) fruit and vegetables - fibre, folate, Vit C, Vit E, flavonoids etc (contain biologically active compounds) tea and coffee berries and nuts antioxidants spices
How does obesity and physical inactivity affect cancer risk
up by 5.5% in all cancers
main are colorectal and breast
What are the obesity-related mechanisms that increase cancer risk?
signalling lipids inflammatory cytokines adipokines insulin/IGF fatty acids
Describe one obesity-related mechanism - obesity-inflammation-aromatase axis
inflammation and parallel increase in the levels of aromatase expression or activity –> increase oestrogen
increase activty of NF-kappaB transcription factor
How does physical activity reduce cancer risk?
decrease hormones levels (insulin and oestrogen)
decrease levels of inflammation
Is there a correlation between alcohol and cancer?
yes
- by various processes
What cancer does asbestos cause?
mesothelioma - cancer of pleura
prolonged inhalation of asbestos fibres can cause serious and fatal illnesses
What cancer are the following populations at risk off and what were they exposed to?:
- japanese atomic bomb survivors
- underground miners
- radiologists
- luminous dial painters
- general public
- japanese atomic bomb survivors = radiation –> leukaemia
- underground miners = radon –> lung cancer
- radiologists = radiation –> skin cancer
- luminous dial painters = radium –> bone cancer
- general public = solar radiation –> melanoma
What are the challenges in studies of diet and life-style factors?
What is a better, more direct, way to assess cancer risk?
Results of studies are often contradictory because multifactorial exposure is difficult to measure
e.g. food habits change over time
Better way = look at molecular links instead
What is the bad luck hypothesis?
That variation in cancer risk among tissues can be explained by the number of stem cell divisions
- cancers happen due to errors in cell division
- stem cells responsible for initiation of cancer
- linear correlation meant there was no environmental effect!
What happened when the bad luck hypothesis was critically analysed?
lots of mistakes found
now discounted
