Cancer Epidemiology: An

Cancer Epidemiology: an overview

A Global Concern • 1990 60 million deaths

2000

2010

80 million deaths

2/3 in developing countries With 5% of the resources to deal with the problem 40 million of these deaths are preventable

A Global Concern • 9 Million new diagnoses each year • 5 million deaths each year • 10% of all deaths in the world each year • Usually regarded as a problem of developed countries • More than half of of all cancers are seen in ¾ of the world’s population who live in developing countries

Epidemiology of Cancer • Studies on the epidemiology of cancer break down into two basic areas. • The biology/molecular genetics of cancer. • The sociology of cancer. • Understanding both of these areas in critical for cancer control.

Basic biology of cancer • Many diseases – One disease process. • A disorder of cellular growth and differentiation. • 100 different cancers • Affects any cell in the body that can undergo mitosis/cell division. • Cancer has links to other disease processes

Biology of Cancer • Some infections cause cancer – Schistosomiasis: bladder cancer – Liver fluke (Clonorchis sinensis): gall bladder cancer

• Toxic causes and cancer – Lung cancer (mesothelioma) exposure to asbestos

• Despite all this cancer is fundamentally a genetic disorder. • Cancers are only a problem because they spread or metastasise

Biology of Cancer TUMOUR GROWTH

HOST RESISTANCE

OUTCOME

Biology of Cancer • Tumours do not grow freely in the human host. • There is a defence or “host resistance”. • Resembles a defence against an infection. • Transformation, invasiveness, metastasis malignancy, will all depend upon interaction with the host defences. • This balance will change during the life history of the tumour.

Biology of Cancer Implications • Regard cancer as a “Rule” of thirds. • 1/3 are preventable • 1/3 are curable (1/2 in developed countries) • These numbers depend on – Effective and comprehensive screening – Early diagnosis

• Leads to greater curability

The “Rule” of Thirds • This is the case because most cancers are acquired (somatic). • Only about 5% of all cancers are inherited. • If cancers are acquired (from external influences) they are potentially avoidable.

The Sociology of Cancer • Cancer is a lifestyle disease • Carcinogens arise as a consequence of lifestyle. – Conditions of living – Conditions of work

• Carcinogen exposures arise from two situations – Where people live – Changes people make in the world

Sociology of Cancer • Where people live. • Geographic and temporal variability – Habits • Smoking ----- Lung cancer. • Diet ------------ Stomach and colon cancer. • Food preservatives --------- Stomach and liver cancer.

• Environmental hazards – Viruses and liver cancer.

Sociology of Cancer • Changes people make in the world – (Industrialisation) • Ionising radiation • Chemicals from manufacturing processes. • For example (Ionising Radiation): • Latter part of 19th century half of certain groups of mine workers in central Europe died of lung cancer • Also occurred in early 20th century USA • Radioactivity in the bedrock of these mines caused the cancer

Sociology of Cancer • Example (manufacturing) • Dyestuffs (betanaphthylamine) caused bladder cancer in Europe and USA until occupational health initiatives stooped its use. • Reoccurring in Southern Asia where industrialisation has exported this technology to new areas. • New cases of mesothelioma in turkey due to use of asbestos like products

Sociology – Implications for Cancer Control • Importance of lifestyle changes. • Importance of prevention and screening. • The need for a public health strategy fro cancer control – At a national level – Balanced programme of Prevention, Screening, Early diagnosis, treatment, palliation

Implications for cancer control • These factors mainly depend on changes in the behaviour patterns of humans. – Addictions to drugs, smoking, alcohol, food. – Sexual behaviour

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Examples: – Oral cancer and tobacco chewing – Lung cancer and smoking – Cervical cancer and sexual promiscuity

• Major area of research is how to change behavioural patterns to promote health and prevent disease and cancer.

Biological Factors and cancer aetiology • Four classes of external agents in carcinogenesis. – – – –

Physical Chemical Biological Diet

• Physical Agents – Ionising radiation: Cosmic and earth sources (energy production). – Cumulative exposure from medical medical and diagnostic procedures.

Biological Factors and cancer aetiology • Ionising radiation – Breast, leukaemia, lung, thyroid, stomach, colon, bladder are common radiation induced tumours.

• Non-Ionising radiation: Solar UV light and tanning industry – All forms of skin cancer.

• Particles: – Air Pollution and other factors • Asbestos dust and mesothelioma

Biological Factors and cancer aetiology • Chemical Agents are very important in carcinogenesis. • Concepts of Promotion and Initiation have been developed in chemical exposure. • Industrial exposure. • Chemical exposure due to habits.

Biological Factors and cancer aetiology • Chemical exposure is perhaps one of the areas that provides a mechanism of control. • Many chemical exposures are as a result of; – Habits (smoking): lung cancer – Industrial processes: Many cancers – Medicinal practices (diethylstilbestrol to prevent abortion (can cause vaginal cancer) – Alcohol: head and neck cancer

Chemical Agents Exposure

Chemical

Site of Cancer

Insecticide spraying

Arsenic

Skin

Nickel refining

Nickel

Paranasal Sinuses

Chromium plating

Chromium

Lung

Shale oil production

Polynuclear Aromatic Hydrocarbons

Scrotum

Vinyl chloride production

Vinyl Chloride

Liver

Gas retort work

naphthylamine

Bladder

Tyre manufacturing

Benzene

Leukaemia

Biological Factors and cancer aetiology • Biological Agents are central to the development of many cancer: – Hepatitis B virus: Liver cancer – Epstein Barr virus: Lymphomas and some nasal/pharyngeal cancer – Human Papilloma virus 16: Cervical cancer – Schistosomiasis: Bladder cancer – Liver fluke: Gall bladder cancer

Biological Factors and cancer aetiology • Dietary factors – Dietary fat – Food preservatives – Protective substances in food and diet.

• These factors mainly relate to lifestyle and habits. – High fat /low fibre diet associated with colorectal cancer – Food preservative (nitrites) associated stomach cancer

• Many food are associated with health and protection against cancer – Cruciferous vegetables, whole grain (fibre), citrus fruits

Social Factors and Cancer Causation • Social class – Socioeconomic gradient

• Occupation – Industrial hazards

• Medical Services and care – Radiation and medications

• Lifestyle – Habits and food handling

• Air and water pollution

Summary - Risk factors • Smoking • Dietary factors • Obesity • Exercise • Occupation • Genetic susceptibility • Infectious agents

• Reproductive factors • Socioeconomic factors • Environmental pollution • Ultraviolet light • Ionising radiation • Prescription drugs • Electromagnetic fields