Epidemiology of cancer

Question 1

Differentiate between mortality and incidence

Answer 1

Incidence= how many new cases there are in a given time period
Mortality= how many people die in a given time period

The two DO NOT coincide- e.g skin cancers are quite common (so have a high incidence) but they are not very lethal ( so low mortality).
Pancreatic cancers are leukaemia are highly lethal (so very acute and have a low incidence).

Question 2

What are the leading causes of deaths in the world (2012)

Answer 2

IHD
Stroke
COPD
Lower Respiratory conditions
Tracheal, bronchal, lung cancers
HIV/AIDS
Diahorreal diseases
D.M
Road injury
Hypertensive heart disease
Prematurity
T.B

Question 3

What is meant by the epidemiological shift

Answer 3

Causes of death in the world have shifted from traumatic and infectious diseases to non-communicable diseases (CVD and cancer).
Non-communicable diseases are responsible for 70% of deaths in the world.

Question 4

What is happening to death rates from CVD and cancer in all age groups

Answer 4

o Death rates from CVS disease have dropped over the years.

o Death rates from cancer have remained stable/increased-slightly over the years

This is most likely to improved prevention (reducing incidence) and improved therapies (reducing mortality).

Question 5

If you exclude war and the dissolution of the soviet union, what has been observed for the first time in the USA in the 19th century

Answer 5

The life expectancy of the white poor has decreased (due to alcohol and drug abuse, as well as the use of excessive pharmaceuticals).

Epidemiological effects tend to be observed first in america and then spread to the rest of Western Europe..

Question 6

What are incidence rates for cancer normally given in

Answer 6

Deaths per 100,000.

Question 7

What is happening to incidence rates of cancer in low-income/ traditional countries

Answer 7

The incidence rates of cancer in Ireland, Belgium, France, U.K, Lithuania, Austria, Japan and China are at least 2-fold greater than those in Trinidad and tobago, Nigeria, Egypt, India, UAE and saudi arabia.
However, as these countries become more westernised and exposed to cancerous risk factors- their incidence of cancer increases too- so the incidence rates of cancer in the world converge because of the epidemiological shift.

Question 8

List the examples of geographical variations in incidence rates of cancer worldwide

Answer 8

Melanoma common in NZ/Australia- not so common in China
Prostate common in North America, not so common in China
Lung common E.Europe, not so common in W.Africa
Colorectal common in Japan, not so common in Middle Africa
Esophageal common in China, not so common in W.Africa
Liver common in china, not so common in South Central Asia
Bladder common in S.Europe, not so common in Melanesia
Breast common in N.America, not so common in Middle Africa
Non-Hodgkin common in N.America, not so common in China

Question 9

When comparing geographical incidence rates, what 2 things must you consider to ensure that the data observed is causally correlated.

Answer 9

That the data is credible- this is achieved by the WHO regulating the quality of each national database/register of cancer incidence/mortality.
That there are no genetic influences and that the effects are environmental - migrant studies.

Question 10

Why may the incidence of melanoma be higher in Australia

Answer 10

Environmental - more exposure to sunlight

Genetic- fair people deported from the U.K have a higher genetic suceptibility to mealnomas.

Question 11

When comparing incidence rates of cancer between different countries, what must be controlled

Answer 11

As cancer is a disease of old age, the distribution of ages in the populations studies must be similar.

Question 12

What did the migrant study in Japan regarding stomach cancers demonstrate

Answer 12

The Japanese had a high mortality from stomach cancers, whereas the USA had a low mortality.
The Japanese that moved from Japan to Hawaii had a reduced mortality rate (closer to that of americans).
Population genetics cannot explain this (change occured to quickly for the genes to catch up) therefore environmental changes must explain this.
For example, the Japanese swithced to a diet rich in red meat and alcohol, which increased their risk of stomach cancer.

Question 13

How can we interpret migrant studies

Answer 13

If cancer is purely hereditary (e.g rare forms of genetic paediatric cancers) then their mrotality rate will be persistent in all countries.
However if the cancer is mostly caused by environmental factors, then their susceptibility to cancer will increase when they move to high risk countries as they will be exposed to riskier diet changes, lifestyles and environmental pollutants.

Question 14

What has happened to the mortality of lung cancers

Answer 14

Increased rapidly to smoking

Now plateuing, decreasing as smoking becomes less common

Question 15

What has happened to the mortality of stomach cancers

Answer 15

Decreased- perhaps due to better preservation of foods- thus reducing infection from H.Pylori

Question 16

Summarise migrant studies

Answer 16

§ Rapid change in risk following migration à lifestyle and environmental factors act late in carcinogenesis.

§ Slow change à exposures early in life are more relevant.

§ Persistence of rates à genetic susceptibility is important in determining risk.

Question 17

Describe the trends in cancer incidence worldwide

Answer 17

§ Incidence is increasing for common cancer sites in both high-income (with plateau/decrease) and low-income countries – effects of earlier diagnosis, screening and changes in risk factors.

§ Rapid increases in incidence may be due to the introductions of official screening procedures.

o High income countries tend to show an increasing and then rapid increase followed by a plateau of cancer incidence due to introduction of screening procedures.

Question 18

Describe the trends in cancer mortality worldwide

Answer 18

§ Mortality is decreasing in high-income countries but NOT low-income.

o Total burden of cancer is increasing.

§ If changes in cancer incidences or mortality are too rapid, there cannot have been genetic changes.

Decreasing in high-income due to better screening methods (screen cancers before malignant changes- thus a better prognosis of treatment). Also better treatment and reduction in risk factors.

Increasing in low-income- reduced detection and access to medical care, increased burden of cancer (both those caused by infection- Cervical and stomach)- but also those caused by a western lifestyle- breast- prostate

Question 19

What is important to remember about the incidences and mortality of cancers in recent years

Answer 19

Incidence is increasing for common cancer sites in both high-income (now with plateauing and even decreases) and low-income countries (e.g. breast, colorectum, prostate) – effects of earlier diagnosis, screening, changes in risk factors? Mortality is decreasing in most high-income countries (e.g. -23% between 1990 and 2008 in US men), not in low income countriesTotal burden is increasing because of demographic changes (ageing populations, increasing size), and Westernization of lifestyles

Question 20

What do migrant studies show about the nature of most cancers

Answer 20

90-95% of all cancers are not hereditary
Inherited conditions account for only 5-10% of all cancers- these inherited mutations increase your susceptibility to certain cancers

Question 21

What can the term ‘genetic’ mean in cancers

Answer 21

Acquired changes in DNA (environmental)
Hereditary changes in DNA- which can make you susceptible to environmental changes which can change your DNA- acquired mutations
Essentially, cancer is a genetic disease due to changes in DNA.
e.g may have a mutations which means you don’t have the enzyme to repair p53 mutations, so when exposed to sunlight- you get skin cancers.

Question 22

Name some inherited conditions that can lead to cancer

Answer 22

Hereditary retinoblastoma- retinoblastoma (Rb1 gene- inherit one mutation, acquire the second)
Xermodoma pigmentosum- skin- faulty enzyme to repair p53 mutations.
Wilms’s tumour- kidney
Li-Fruameni syndrome - Sarcomas, brain, breast, leukaemia
Familial Adenomatous polyposis- colon, rectum
Paget’s disease of bone - bone
Fanconis’s aplastic anaemia- Leukaemia, skin, liver

Question 23

List the contribution of lifestyle factors to the attributable risk of cancer

Answer 23

Population attributable risks percent:
Smoking			29-31 
Diet				20-50
Alcohol			            4-6
Infection 			10-20
Occupation 			2-4
Reproductive hormone	           10-20
Pollutants- 1-2

Question 24

Explain the issue with measuring the impact of environmental pollutants on cancer risk

Answer 24

Methodological problem:
Lifestyle/behaviours can easily be measured in questionnaires- allowing for comparisons between groups.
However, everyone is exposed to air pollution- so it’s hard to compare between exposed and unexposed
E. G – PCBs or P-FASA, which are components of plastics, are everywhere- in our blood and accumulate in tussues and fat- this involves collecting biological samples- and so these studies are much more complex- not sure about whole picture, and whole picture may be different when tools to study environmental pollutants effectively become available.
New field of investigation- exposome- totality of exposures in the environment.

Question 25

What behaviours did Parkin recommend

Answer 25

=> 5 servings of fruit and vegetables; =>23 g/day of fibers; <=6 g/day of salt; BMI<=25 kgm-2; physical activity=> 30 min 5 times/week; breastfeeding at least 6 months

Question 26

Describe the current Parkin’s estimate of preventable cancers in the UK

Answer 26

14 risk factors and 18 cancer sites have been considered. The result is that 45% of cancers in men and 40% in women could have been prevented had risk factors been reduced to the optimal levels or eliminated (like tobacco). Reduction/elimination of the same risk factors would lead to a substantial reduction also of cases of cardiovascular disease, renal disease, hepatic disease, diabetes and possibly some neurological diseases.

Need more reliable data about pollutants to complete the picture.

Question 27

Describe the impact of smoking on cancer risk

Answer 27

Smoking accounts for at least 30% of all cancer deaths

Smoking is associated with increased risk for at least 15 types of cancers

Smoking causes 90% of lung cancer deaths in men and80% in women

Question 28

In which organs can smoking cause cancer

Answer 28

Throat
Mouth
Larynx
Blood
Oesophagus
Stomach
Lung
Kidney
Pancreas
Cervix
Bladder

Question 29

Which dietary factor may be protective against colon cancer

Answer 29

Statistical model adjusted for : energy, height, weight, physical activity,
alcohol and tobacco

Fibre

Question 30

Describe the impact of alcohol on cancer risk

Answer 30

Oral cavity, pharynx, larynx, oesophagus, liver
all types of alcohol
mechanisms poorly understood
synergism with tobacco
balance with preventive effect for CHD

Question 31

Describe how obesity/high BMI can increase your cancer risk

Answer 31

Inflammatory disease- chronic inflammation is a hallmark for cancer
Obesity increases your risk of post-menopausal breast cancer, endometrial cancer and pancreatic cancer.

Question 32

What are the world cancer research funds guidelines for dietary prevention

Answer 32

1. Be as lean as possible without becoming underweight;
2. Be physically active for at least 30 minutes every day;
3. Avoid sugary drinks. Limit consumption of energy-dense foods (particularly processed foods high in added sugar, or low in fibre, or high in fat);
4. Eat more of a variety of vegetables, fruits, wholegrains, and pulses such as beans. Basing our diets on plant foods, which contain fibre and other nutrients, can reduce our risk of cancer;
   . Limit consumption of red meats (such as beef, pork and lamb) and avoid processed meats. To reduce your cancer risk, eat no more than 500g cooked weight (700-750g uncooked) per week of red meats, like beef, pork and lamb, and avoid processed meat such as ham, bacon, salami, hot dogs and some sausages;
5. If consumed at all, limit alcoholic drinks to 2 for men and 1 for women a day;
6. Limit consumption of salty foods and foods processed with salt (sodium);
7. Don’t use supplements to protect against cancer. To reduce your risk of cancer, choose a balanced diet with a variety of foods rather than taking supplements.

Question 33

What can increase the risk of breast cancers

Answer 33

Both endogenous and exogenous sex hormones

Question 34

What is the western lifestyle

Answer 34

Energy dense diet, rich in

- fat, 
 	- refined carbohydrates 
- animal protein - Low physical activity - Smoking and drinking

Question 35

Describe the consequences of a Western lifestyle

Answer 35

Consequences:
	- Greater adult body height 
	- Early menarche
	- Obesity
	- Diabetes
	- Cardiovascular disease
	- Hypertension
and cancer!

Question 36

Describe the cancers worldwide attributable to infection

Answer 36

~16% cases of cancer likely caused by infectious agents worldwide
25% in Africa
<10% in Europe (1 in 33 in UK)

Question 37

List some of the infectious causes of cancer

Answer 37

o E.G. HPV 16 and 18 (cervix cancer, also head and neck), EBV (Hodgkin’s/Burkett’s Lymphoma), HCV/HBV (liver cancer), H. pylori (stomach cancer).