Cancer 11: Epidemiology of Cancer

Question 1

Relation between incidence and mortality in cancer

Answer 1

• sometimes there is high incidence and low mortality in cancers that are not lethal
• if incidence and mortality are very close the cancer is very lethal (e.g. pancreatic cancer and some acute leukemias)

Question 2

What are the most common causes of death?

Answer 2

1. cardiovascular disease
2. cancer (all cancers collectively)
3. other

Question 3

What affects incidence and mortality?

Answer 3

Prevention affects incidence.

Treatment affects mortality.

Question 4

MIgrant studies

Answer 4

• Extent and rate of change that are informative
• A rapid change in risk following migration implies that lifestyle/environment factors act late in carcinogenesis
• A slow change suggests that exposures early in life are the most relevant
• Persistence of rates between generations suggests genetic susceptibility is important in determining risk

=> allows to see if genetic or environmental factors are more important in developing the cancer.

Question 5

Why did the incidence of stomach cancer decline over the last decades?

Answer 5

-> Refrigerators

Better storage of food -> less bacteria (H. pylori) -> less stomach cancer

Stomach cancer is caused by environmental factors, not inherited.

Question 6

How has the incidence of cancer changed in the western world?

Answer 6

• it was increasing but has now plateaued.
• This could be due to a development in diagnostic tools, detect cancer in earlier stages.
• Some of the incidence is due to PSA screening and mammography.
• Exposure to risk factors is another reason (e.g. less smoking)

Question 7

How has mortality due to cancer changed?

Answer 7

• it has decreased
• this is due to better therapies
• this is also due to better screening and detecting cancer at earlier stages -> more curable.

Question 8

Incidence, Mortality and Burden of cancer - Summary

Answer 8

• 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 countries
• Total burden is increasing because of demographic changes (ageing populations, increasing size), and Westernisation of lifestyles

Question 9

Success rate for treating leukaemia in children?

Answer 9

• 80-90% in the western world

- in poor countries this is lower because they don’t have access to the treatments necessary.

Question 10

How are high and low income countries different epidemiologically?

Answer 10

• low income countries are still in the epidemiological transition
• more infection based cancers.
• no screening
• less access to more effective strategies

Question 11

What are some hereditary conditions that lead to cancer?

Answer 11

• hereditary retinoblastoma -> retinoblastoma
• xeroderma pigmentosum -> skin cancer (they cannot repair the damage, they need exposure to sunlight to develop cancer)
• Wilm’s tumour -> kidney
• Familial adenomatous polyposis -> colon, rectum cancer
• Paget’s disease of bone -> bone
• Fanconi’s aplastic anaemia -> leukemia, liver, skin
• Li-Fraumeni syndrome -> sarcomas, brain, breast, leukemia

Question 12

What are the main RFs for cancer?

Answer 12

Smoking	: 29-31
Diet	: 20-50
Alcoho:  4-6
Infection: 10-20
Occupation:	2-4
Reproductive hormone: 10-20

Question 13

Smoking as a RF for cancer

Answer 13

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 and 80% in women

Question 14

RFs for colorectal canccer

Answer 14

• red meat

- you should eat fibre from fruit and veg

Question 15

Alcohol as a RF for cancer

Answer 15

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

Question 16

Obesity and cancer

Answer 16

• obesity is a RF for cancer
• obesity is an inflammatory disease
• Many inflammatory cytokines, there is chronic inflammation which is one of the hallmarks of cancer.

Question 17

Guidelines for dietary prevention of cancer

Answer 17

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;
5. 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;
6. If consumed at all, limit alcoholic drinks to 2 for men and 1 for women a day;
7. Limit consumption of salty foods and foods processed with salt (sodium);
8. 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 18

Westernisation of lifestyle and cancer

Answer 18

Western Lifestyle:

• Energy dense diet, rich in
  
  • fat,
    - refined carbohydrates
  • animal protein
• Low physical activity
• Smoking and drinking

Consequences:

- Greater adult body height 
- Early menarche
- Obesity
- Diabetes
- Cardiovascular disease
- Hypertension

Question 19

Name some pathogens and what cancers they can cause. How much cancer is due to infections?

Answer 19

HPV (16,18) -> Cervix, Head and Neck
EBV -> Hodgkin’s Lymphoma, Burkitts
HCV, HBV -> Liver
H. Pylori -> Stomach

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

Question 20

Key Points

Answer 20

• Cancer is a leading cause of death

1. The epidemiology of cancer tells us that cancer incidence is related to:
   Age
   Common environmental causes
   Geographical variation and secular trends
   There are several well defined risk factors for cancer, including smoking, diet and alcohol consumption.
2. The process of carcinogenesis is important in understanding the development of cancer. Important factors involved in this process include chemical carcinogens, radiation and oncogenic viruses
3. Inherited / familial cancers are rare, but have provided valuable information in understanding the process of carcinogenesis.