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Epidemiology of Cancer
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Collective term that describes over 100 different forms of the disease
Chronic & degenerative disease. Results from genetic changes in a cell
and/or the failure of the body’s immune defenses
Cancer Terms
Cancers are named according to the type of tissue from which they
develop.
Carcinoma – arise from the epithelial tissue, which lines and covers
internal and external body surfaces. Carcinomas develop most frequently
in the skin, large intestine, lungs, stomach, prostate gland cervix, or breast.
Comprise most adult cancers
Cancer Terms
Sarcoma – cancers that arise from the connective tissue or muscle tissue.
Leukemia – cancers of the blood and related cells.
Lymphomas – cancers of the lymphatic system, the network of vessels and
nodes that transport and filters tissue fluid.
Cancer biology
Cancer is a genetic disease
It follows (often extensive) genetic injury to cells
The cells must survive the injury to develop into cancerous cells
They must grow, usually extensively, to lead to clinically apparent cancer
Cancer cells behave differently from non-cancer cells because of the
genetic material within the cell.
Normal cells have the capacity to transform energy and transmit
information from generation to generation.
Basic Progression Model
Cell Growth and Division. Cell Cycle - all cells (normal and abnormal) go
through 5 phases of development. The cell cycle time is the time required
for one tissue cell to divide and reproduce into two identical daughter cells.
Lecture [6]
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G1 phase –RNA and protein synthesis & cell growth occurs. This is when
the cell actively begins the cell cycle and lasts a few hours to several days.
Cell Cycle
S phase - DNA synthesis & chromosomes replication occurs. The 2 sets of
chromosomes contain all of the cells genetic information. This lasts
between 7-20 hours.
G2 phase - premitotic phase, DNA synthesis complete, mitotic spindle
forms. Lasts 1-4 hours.
Cell Growth and Division
Mitosis - Cell division occurs. Two daughter cells that contain all of the
cells genetic information.
G0 phase - Resting or dormant phase of cells. These can be dangerous cells
that are not actively dividing but have the future potential for replication.
The Global Cancer Burden
In the year 2000, malignant tumors were responsible for 12% of all deaths
worldwide.
In 2000, 5.3 million men & 4.7 million women developed a malignant
tumors, and altogether 6.2 million died from the disease.
Cancer rate could further increases by 50% to 15 million new cases in the
year 2020.
53% of new cancers cases in developing countries.
57% of cancer deaths in developing countries.
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THE INCIDENCE OF CANCER IN 1988 ACCORDING TO LOCAL REGISTRY
WAS 11/100000 OF POPULATION. IN 1998 THE INCIDENCE INCREASED
TO 75/100000, WHILE IN 2001 THE INCIDENCE RAISED TO 116/100000.
Incidence rates/100000 in Basrah
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Proportion of children below five years with leukemia in Basrah 1990-
2000
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Year total <5 %
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15 2 13.3
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15 5 33.3
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14 5 35.7
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25 10 40.0
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24 10 41.7
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24 10 41.7
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24 10 41.7
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30 14 46.7
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60 34 56.7
Ref.: Dr. Alim AH Yaqoub, Dr. Imad Al-Saadon, Dr. Genan G Hasan
Distribution
Age
Cancer strikes at any age
It kills more children 3-14 than any other disease.
Cancer strikes more frequently with advancing age. (>65)
Distribution
Sex
Higher incidence in men than in women (past exposure to tobacco
smoking, alcohol consumption, and hazardous occupations).
Thyroid & gallbladder cancers are more common in women (diet,
overweight, estrogen). The mean age of females at onset is higher than
males.
Geographical distribution
Higher in industrialized sectors and nations.
Place: etiologic factors present in the biologic, chemical, physical, or social
environment.
Stomach cancer in Britain: smoking, diet, physical activity.
Burkett’s lymphoma in Africa: malaria
Skin cancer in Australia: sunlight exposure.
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Time trend
Changes of type/magnitude of social, biological, physical, and chemical
factors with passage of time.
Artificial variation:
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improvement in diagnosis or recording
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Changes in diseases classification, reactivation of screening tests or use of
more sophisticated techniques e.g. MRI.
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Bias in recording e.g. for political reason
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Aging of the population (increased susceptible individuals).
Real increase
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Changes in the population lifestyle in relation to diet, smoking, exercise,
type of work, ..etc.
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Introduction of a new causative agent: DU, AIDS.
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Changes in case fatality: low immunity, bad management.
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Maladaptation to social changes: industrialization, political unrest.
Race/Religion and Cancer
Blacks get cancers more common than Whites.
Cervical cancer is rare in Jewish women: Avoidance of multiparteners.
Determinants of malignant Neoplasms
Neoplasms are generally the result of an interaction between two classes
of determinants genetic & environmental. Four broad categories of cancers
caused by different genetic-environmental interaction can be identified.
1. Cancers in which genetic factors determine their occurrence, the
heritable forms of cancer e.g. familial multiple polyposis coli, familial
neurofibromatosis. They represent 1-2% of all neoplasms.
2. Cancers produced by environmental agents.
3. Cancers produced by combined environmental and genetic factors, e.g.
Xeroderma pigmentosum risk of melanoma
Categories 2&3 cover the greatest majority of all malignant neoplasms.
4. Cancers independent of genetic and environmental factors mainly
resulting from somatic mutations. They represent 20-30% of all cancers.
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Established environmental determinants
Radiation:
a- Non-ionizing radiation (Sun light): ultraviolet radiation such as in sun:
Basal cell carcinoma of face & neck, squamous cell carcinoma of the
exposed surfaces and lips.
b- Ionizing radiation (Diagnostic procedures):
leukemia (acute & chronic myeloid leukemia)
Established environmental determinants (contin.)
Smoking:
- Smoking is causally associated with cancer at several sites such as lungs,
mouth, pharynx, larynx, esophagus, pancreas and kidneys.
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Tobacco smoke has been shown to cause cancer in experimental animals.
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Even low level of exposure to passive smoking may increase the risk of
lung cancer.
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Smoking related cancers represent about 30% of all cancers in the
developed countries.
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Environmental tobacco smoke is associated with a 35-50% increase in
lung cancer.
Established environmental determinants (contin.)
Alcohol:
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Alcohol is associated with the occurrence of cancers of the mouth,
pharynx, larynx, and esophagus.
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In doses capable of causing liver cirrhosis, alcohol can increases the risk
of liver cancer
Established environmental determinants (contin.)
Biological agents:
a- Parasites: schistosoma haematobium is associated with bladder cancer.
b- Liver flukes: clonorchis sinensis & opistorchis viverrini are associated
with cholangio-cellular ca.
c- Viruses:
-Hepatitis B virus is associated with primary hepatocellular carcinoma.
- Epstein Bar virus is associated with endemic Burkett lymphoma ,
nasopharyngeal carcinoma &Hodgkin diseases.
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- Herpes virus is associated with cervical ca.
- AIDS virus is associated with Kaposi sarcoma & lymphoma.
Established environmental determinants (contin.)
Some chemical agents:
There are a large group of chemical agents for which epidemiological
evidence supported by experimental evidence of carcinogenicity in human
had been established, e.g. Asbestosis, Benzene, Benzidin, Methyl ether,
Mustard gas, Vinyl-Chloride.
Established environmental determinants (contin.)
Obesity:
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Obesity increases the risk of endometrial cancer
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It probably increases the risk of postmenopausal breast cancer, renal
cancer, colon cancer, and cancers of the gall bladder
Established environmental determinants (contin.)
Diet:
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Certain dietary pattern may be causally related to cancer.
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High correlation between dietary fat & the occurrence of cancer in many
sites, like colorectal, breast, endometrial, prostate, lung, and pancreatic
cancers.
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There is a strong & convincing evidence that diet rich in vegetables and
fruits decreases the risk of many cancers and perhaps cancer in general,
e.g. decreases risk of mouth, colorectal, pharyngeal, esophageal, lung and
stomach cancers.
Diet: (contin.)
- Minerals: diet deficient in Iodine probably increases the risk of thyroid
cancer.
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Vitamins: There is sustained and consistent evidence that high intake of
vitamin A and Vit. C decreases the risk of cancers of various sites, e.g. Vit. A
decreases the risk of lung cancer.
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- Diet high in salted food and salt itself probably increases the risk of
stomach cancer, salted fish increases the risk of nasopharyngeal cancer
- Food contamination by various types of mycotoxins (metabolites of
moulds such as aflatoxins) probably increases the risk of primary liver
cancer.
The mechanisms by which diet is causing cancer include:
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Through ingestion of carcinogens.
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By altering the concentration or duration of contact of carcinogens with
cells in the large bowel.
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Through induction or inhibition of enzymes which affect carcinogen
metabolism.
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Over- nutrition causes obesity.
Post-menopausal hormone use
–Breast cancer risk, Nurses Health Study
THE AIM OF CANCER CONTROL
Reduction of cancer incidence, Morbidity , and Mortality by:
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Prevention
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Early diagnosis
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Treatment
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Palliative treatment
Prevention of cancers
Primary prevention:
primary prevention of some cancers is possible for the following
reasons:
a- The environmental causes of some cancers are sufficiently well
established.
b- Some of the environmental factors are amenable to prevention.
Primary prevention requires changes in diet and related lifestyles which
include the following:
Prevention of breast cancer by treatment of DCIS
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Dietary pattern:
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Advice to consume nutritionally adequate and mixed diet based primarily
on foods of plant origin.
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Promote year-round consumption of a variety of vegetables and fruits.
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Limit consumption of fatty food to not more than 30% of the total energy.
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Limit consumption of salted food. Salt intake should be less than 6 gm/day
for adults.
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Don’t eat food contaminated with mycotoxin as a result of prolonged
storage.
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Use refrigeration &other appropriate methods to preserve food.
Primary prevention (contin.)
Discourage production, promotion , and use of tobacco in any form.
Discourage excessive consumption of alcohol.
Maintaining body weight, and avoid being underweight or overweight.
Maintaining physical activity.
Limit x-ray exposure.
Avoid Occupational Hazards as possible.
Secondary prevention
There are two aspects of secondary prevention:
Early detection of cases as soon as possible after symptoms have been
developed (through community education, e.g. Ca. breast by self
examination).
Early detection in asymptomatic population through a large scale (mass
screening) program.
Tertiary prevention
Treatment of known cases by surgery, radiation, and chemotherapy or
combination.
Pain-relieving palliative treatment.