Lecture 2 - Cancer and Environmental Factors

Question 1

What did a study looking at a cancer risk by country find/

Answer 1

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

Question 2

What proportion of cancer deaths are attributed to non-genetic factors. What are the two most common non-genetic causes of cancer?

Answer 2

75%

tobacco and diet

Question 3

What did the study looking at japanese populations and migrating to hawaii show?

Answer 3

• levels of certain cancer risk changed dramatically postmigration, though genetics hadn’t changed
• shows that environment has a significant effect on incidence

Question 4

What did Pott notice in chimney sweeps?

Answer 4

correlation between soot lodging in the folds of scrotal skin and skin cancer of the scrootum

Question 5

How are carcinogens classified, using the current IARC system?

Answer 5

• 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

Question 6

What are the 3 aspects of risk assessment?

Answer 6

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

Question 7

What can be included in the concept of environmental health affecting human health?

Answer 7

diet, lifestyle, infectious disease

outdoor and indoor air pollution, soil and drinking water contaminants

Question 8

What makes up outdoor air pollution?

What are the sources of air pollution?

Answer 8

particulate matter
nitrogen/sulphur dioxide
ozone gas
CO
polycyclic aromatic hydrocarbons (PAHs)
SOURCES= transport, industry, farming, cooking/heating, natural pollutants

Question 9

elevated urban/rural ratios with many cancer, such as…

Answer 9

mouth and throat
nasopharunx
oesophagus
stomach
colon
breast
bladder 
prostate

Question 10

Describe ‘linking nicotine addiction and lung cancer through tobacco-smoke carcinogens’

Answer 10

Nicotine –> tobacco carcinogen exposure by addiction –> DNA adducts –> mutations –> lung cancer

Question 11

What does the dose-exposure graph look like for smoking and chronic lung disease, lung cancer, CHD and CVD

Answer 11

linear correlation

Question 12

What is the direct and indirect effect of diet on cancer risk

Answer 12

direct = particular components added to the diet that are responsible to increased or decreased risk
indirect = effect involving the balance of the diet

Question 13

What foods are probable carcinogens? Who was this announced by? What was their evidence?

Answer 13

processed and red meats
WHO
800 epidemiological studies

Question 14

What are examples of food that fight cancer?

Answer 14

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

Question 15

How does obesity and physical inactivity affect cancer risk

Answer 15

up by 5.5% in all cancers

main are colorectal and breast

Question 16

What are the obesity-related mechanisms that increase cancer risk?

Answer 16

signalling lipids
inflammatory cytokines
adipokines
insulin/IGF
fatty acids

Question 17

Describe one obesity-related mechanism - obesity-inflammation-aromatase axis

Answer 17

inflammation and parallel increase in the levels of aromatase expression or activity –> increase oestrogen
increase activty of NF-kappaB transcription factor

Question 18

How does physical activity reduce cancer risk?

Answer 18

decrease hormones levels (insulin and oestrogen)

decrease levels of inflammation

Question 19

Is there a correlation between alcohol and cancer?

Answer 19

yes

- by various processes

Question 20

What cancer does asbestos cause?

Answer 20

mesothelioma - cancer of pleura

prolonged inhalation of asbestos fibres can cause serious and fatal illnesses

Question 21

What cancer are the following populations at risk off and what were they exposed to?:

1. japanese atomic bomb survivors
2. underground miners
3. radiologists
4. luminous dial painters
5. general public

Answer 21

1. japanese atomic bomb survivors = radiation –> leukaemia
2. underground miners = radon –> lung cancer
3. radiologists = radiation –> skin cancer
4. luminous dial painters = radium –> bone cancer
5. general public = solar radiation –> melanoma

Question 22

What are the challenges in studies of diet and life-style factors?
What is a better, more direct, way to assess cancer risk?

Answer 22

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

Question 23

What is the bad luck hypothesis?

Answer 23

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!

Question 24

What happened when the bad luck hypothesis was critically analysed?

Answer 24

lots of mistakes found

now discounted