Environmental Factors and Cancer Flashcards
What are environmental factors, give examples
- Environmental Factors = Non-genetic factors that increase incidence of certain cancers.
- Diet
- Lifestyle choices
- Infectious disease
- Outdoor and indoor air pollution
- Soil and drinking water contaminants
How do Geographic variations in cancer incidence and death rates highlight how environmental factors contribute to incidence
- The incidence of cancers around the world varies.
- E.g. Skin cancer in Australia is very high compared to Japan (155% higher RR).
- 2 factors contribute to this - Hereditary factors and environmental factors.
What do we use to investigate variations in the incidence of cancers and give examples
Using migratory populations
- for example we can compare the Incidence of common cancers in:
- Japanese populations in Osaka
- A migratory Japanese population in Hawaii (USA)
- Native Hawaiian Caucasian population.
Example of stomach cancer:
- Is very high in Japan
- However within one generation of migration to Hawaii, the Japanese population has a low incidence of stomach cancer.
- Example of Breast cancer:
- Low rate in Japan
- However when they migrated to Hawaii the incidence was almost the same as Caucasian American population.
- These examples show that hereditary factors contribute to the incidence of cancer but there are some outside factors that may increase/decreases incidence of cancer – these are environmental factors.
What proportion of cancer deaths can be attributed to non-genetic factors
- One study indicated that of all cancers diagnosed in the USA in 1971, 70% of them could have been avoided if there were changes to non-genetic factors.
- This started a lot of investigation on the contribution of environmental factors on the incidence of cancers.
- Uk 40% of cancers could be avoided through chages to environmental factors
- Tobacco is the biggest environmental contributor to cancer rates
Outline the IARC carcinogen classification system
Group 1: Carcinogenic to humans – strong evidence of cancer risk (e.g. smoking, asbestos).
Group 2A: Probably carcinogenic to humans – limited evidence in humans, sufficient in animals.
Group 2B: Possibly carcinogenic to humans – limited evidence in humans and less than sufficient in animals.
Group 3: Not classifiable – inadequate evidence in humans and animals.
Group 4: Probably not carcinogenic – evidence suggests no risk (very rare).
how are carcinogens characterised
Carcinogens are characterised by their ability to cause cancer when they are applied to the skin of lab mice.
What factors are used to assess the harmful nature of certain carcinogens (3)
- Its potency
- the potential of a given amounts of a substance to cause cancer. eg benzene.
- Type of exposure required to cause harm
- acute or prolonged exposure required and is it avoidable or unavoidable.
- Dose response
- describes trend, indicates what happens if some of the carcinogen is either removed or added.
What makes up outdoor air pollution
- Particulate matter (PM) – PM10 and PM2.5
- Nitrogen dioxide
- Sulphur dioxide
- Ozone gas
- Carbon monoxide
- Polycyclic aromatic hydrocarbons (PAHs)
Air pollution is a big contributor to what cancer
- Particulate matter contents in air pollution causes lung & urinary bladder cancer.
- The below study looked at RR of lung cancer incidence across globe.
- There is increase in RR when there are changes in size of particular matter.
what are the Sources of air pollution
- transport, industry, fossil fuel power stations, farming
- fuels people use to cook and heat their homes
- natural pollutants
What are the sources for indoor air pollution
- The burning of solid fuels to heat homes and to cook with could be a source, but this is less common in the UK.
- The main source of indoor air pollution in the UK is second-hand smoke from cigarettes.
- Most exposure to second-hand smoke happens in the home and is particularly dangerous for children
What does IARC say about air pollution
The IARC classifies outdoor air pollution and particulate matter (PM) as Group 1 carcinogens – meaning they are carcinogenic to humans. There is sufficient evidence that exposure causes lung cancer and links to bladder cancer as well.
What type of studies did the IARC look at to make a report
- Study looks at relative risk of cancer by increase change in particle matter
- They found that there is an increase in risk overall
What are the biological mechanisms behind air pollution
Relative carcinogenesis still needs to be made clear but there is enough evidence to show that air pollution contributes to extensive cell proliferation and cancer
Outline the link between smoking and cancer
Number of deaths among women increased twice in these scenarios showing smoking is harmful not only to person but to people around them.
- This study shows links between smoking and diseases & death.
- 2/3 of all smoker deaths in 50/60/70s are caused by smoking.
- Also the main diseases that are causes of death – lung cancer, CV disease, non-malignant lung disease.
- Number of deaths is increased based on number of cigarettes smoked in a day.
- the earlier the people quit smoking the lower risk of getting the diseases.
Outline the mechanism behind tobacco smoke causing lung cancer
- Tobacco contains loads of carcinogens
- 50 carcinogens
- The middle lane of the schematic shows:
- Nicotine addiction leads to continuous exposure to carcinogens (60/70) found in tobacco that enters the cells in the body.
- When they enter cells in the body, they undergo metabolic activation and produce DNA adducts (covalently bound compounds that damage DNA).
- If they persist it leads to miscoding and so during cell division, DNA adducts contribute to mutagenesis.
- If these mutations happen in specific tumour suppressor genes it will lead to lung cancer.
- The cell has many regulator negative mechanisms to prevent harm via metabolic detoxification or through DNA repair mechanisms but persistent smoking will lead to lung cancer.
What are the direct and indirect effects of diet on cancer risk?
- The direct effects of particular components added to the diet that are an increased or decreased risk of cancer
- The Indirect effects on cancer risk involve the balance of the diet
What is the difference between AICR report and IARC
- AICR reports are based on the expert analyses and assessment of published papers on the links between particular dietary components and cancer risk.
- These links were designated as ‘convincing’ or ‘probable’
- IARC (International Agency for Research on Cancer) evaluates carcinogenicity of agents (including dietary components) according to its own classification.
What diet is most likely to decrease risk of cancer
A Mediterranean diet was most likely decrease risk of pancreatic, colorectal, breast and gastric cancer.
How does colorectal cancer incidence in males in the EU demonstrate the link between colorectal cancer and diet
- This study looked at Colorectal cancer incidence in males in the European Union.
- The difference in incidence and mortality between top and bottom countries is due to dietary patterns.
- Countries on top have a lot of processed and red meat.
- Countries at the bottom have diets that contain a lot of vegetables, beans and fruits
Outline the link between different types of meat and cancer
- Processed meat is meat that was cured, salted or fermented to increase its taste or storage.
- Red meat is fresh/frozen mammalian meat.
- Processed meat is carcinogenic to humans and causes cancer.
How significant is the risk between cancer and tobacco and meat?
- Both tobacco & processed meat do cause cancer.
- However 86% of lung cancers is caused by smoking whilst only 21% of bowel cancer is caused by consumption of processed and red meat.
- 19% of all cancers caused by smoke whereas 3% of all cancers caused by meat.
Which foods fight cancer?
- strong evidence that diets that contain: Fruit and vegetables (fibre, folate, vitamin C, Vitamin E, flavonoids etc.) reduce the risk of getting different types of cancer.
- Fibre – NSP (non-starch polysaccharide) is an important biologically active component
- could be found in fruit and vegetables
- studies that indicate number of colorectal cancers could be reduced if people include fibre in their diet.
Outline the link between obesity and cancer
- Dietary patterns are linked to obesity and physical activity.
- The Relative risks of 7 most common cancers is increased in obese and overweight people.
- There are increases in up to 17,000 cases of cancer in the UK due to being overweight/obese.
- The main contribution is to colon and breast cancer.
