Epidemiology of Cancer
Definitions:
1) Carcinogenesis:
▪
A process whereby a chemical or physical agent
(Carcinogen) causes cancer
2) Teratogenesis:
▪
A process whereby a chemical or physical agent
(Tetratogen) causes a deformed fetuses
3) Mutagenesis:
▪
A process whereby a chemical or physical agent
(Mutagen) that changes (Mutation) the genetic material
▪
Initiates carcinogenesis and some teratogenesis
Abnormal proliferation of cells
Benign: not invade surrounding tissues
Malignant: invade near and far tissues
Topography code: organ or tissue affected
Morphology code: histology features
Incidence rate
Mortality rate
No. of years of life lost
Death certificate: mortality rate
Population based tumor registry : incidence
rate
1.AGE:
Most adult CA arise from basal epithelial cells
of ectodermal or endodermal origin
Most childhood CA are of mesodermal origin
2.SEX
Most major cancers of non-sexual organs
are more in males except:
CA-thyroid
CA –Gall Bladder
ٍ◌Smoking and occupational cancers are more in
males
3.RACE AND GEOGRAPHY
Great variation between races in the
same geographical area and within the
same race at various geographical area
(migrants)
4.TIME TREND
CA-Lung: increasing (increased smoking)
CA-Stomach: decreasing (more fresh and frozen than
preserved food)
CA-Uterus, cervix: decreasing (increased hysterectomy
due to non-CA causes)
CA-Liver: decreasing (better diagnosis of primary sites)
Children CA: decreasing (better treatment)
CA-Colon, Rectum, Pancreas, Breast, Prostate,
Leukemia: not changed
1.TOBACCO SMOKING
Responsible for 30% of CA-deaths
Increases risk of:
CA-lung by 10 times
CA-larynx by 8 times
CA-mouth and pharynx by 4 times
CA-urinary bladder, renal pelvis, ureter, pancrease
by 2 times
It also increases risk of CA- renal parenchyma and
stomach
Attributable risk %
CA-lung:90%
CA mouth, pharynx, larynx, esophagus:
75%
CA-UB:50%
CA-pancrease:40%
4700 chemicals in tobacco smoke 43 are
carcinogenic (cadmium, benzene)
Lung CA epidemic:
In men peak 1990s , declining now
In women, expected to climb
Responsible for
4%
of all male cancer deaths,
and
2%
of all female cancer deaths
It increases risk of :
Hepatocellular cancer
CA-mouth, pharynx, esophagus, supraglottic
cancer
It potentiates effect of smoking
Responsible for 5% of all cancers
International Agency for Research on Cancer (IARC)
▪
Group 1 Human Carcinogen
▪
Benzene and Tobacco
▪
Group 2A Probably Carcinogenic
▪
Acrylamide
▪
Group 2B Possibly Carcinogenic
▪
Acetylaldehyde
▪
Group 3 Unclassifiable
▪
Group 4 Not a Carcinogen
▪
Caprolactam
Responsible for
1%
of all cancer
Alkylating agents: AML, CA-UB
N2 mustard, Arsenic compounds, methoxolone:
CA-skin
Phenacetin: CA-UB, Renal Pelvis
Responsible for
1%
of all cancer
Sources: Natural
Medical
Consumer
External exposure affects:
Superficial organs (thyroid, breast)
Susceptible organs (bone marrow)
Internal exposure:
Inhalation of radioactive dust: CA-Lung
Ingestion of Radium: Bone tumor
Pelvic implants : CA- colon, rectum
Exposure to Iodine
131
: CA-thyroid
Responsible for
10%
of all cancers, and
2%
of
CA-deaths
Sun light : squamous and basal cell Cancers of
skin, and malignant melanoma
Low-frequency electromagnetic field:
leukemia and CA-brain
5 mechanisms are involved in the relation
between diet and cancer
Ingestion of food contaminated by
preformed carcinogen
Aflatoxin B and hepatoma
Artificial sweetener and bladder cancer
Provision of substrate for the formation of
carcinogens in the body or by altering concentration
or duration of contact of carcinogens with colonic
mucosa
Ingested amines and nitrites with CA stomach,
bladder, colon and esophagus
Vitamin C inhibits formation of N-nitroso compounds
and decrease risk of CA-stomach and esophagus
Fiber and CA –colon
High fat and CA-colon, breast , prostate
Induction or inhibition of enzymes that affect
carcinogenesis
Vegetable of Brassicaceae family and CA colon
Production or prevention of formation or
deactivation of short lived carcinogenic
molecular species as Free Radicals
Obesity that act as a tumor promoter by excess
endogenous estrogen increasing risk of
endometerial cancer and postmenopausal
breast CA
Early menarche and late menopause are related
to overnutrition and increased risk of CA breast
and endometerium
Responsible for:
20%
of cancer in developing countries, and
4%
in developed countries
DNA viruses
EBV-African burket lymphoma, nasopharyngeal cancer
HBV-hepatoma
HSV-2 –CA cervix
HPV- CA cervix, vulva, anus
RNA viruses
HIV –kaposi sarcoma, Non-Hodjkin
lymphoma
HTLV-1,2 –T-cell leukemia
HCV-hepatoma
Schistosoma haematobium- CA-UB
Clonorchis sinensis-hepatic angiosarcoma
Opisthorchis virerrini (liver fluke) –cholangial
cancer
Nullipara women have higher risk of CA ovary,
endometrium, and breast
Risk of ovarian and endometrial cancer decreases
with increasing number of pregnancies
Risk of CA-breast increases with increasing age of
having first baby
DES increases risk of CA-vagina in female
offspring and testicular CA in male offspring
Estrogen increases risk of CA endometerium,
while progesteron is protective
OC :
Decreases risk of ovarian cancer
Relation with CA breast is not conclusive
Combined OC decreases risk of fibrocystic disease
and adenoma
Combined OC increases risk of hepatoadenoma,
and focal nodular hyperplasia
Very important in the genesis of many forms of CA
CA breast and prostate aggregate in families
Malignant Melanoma are more in light skinned ,
red hair, blue eyes individuals
CA-stomach is more in individuals with B.group A
Nasopharyngeal CA is more in individuals with HLA-2
A relation between FAP and CA-colon
A relation between Xeroderma pigmentosa and CA-
skin
A relation betwee Bloom”s syndrome and leukemia
Wilm”s tumor and retinoblastoma are genetically
determined
Advice against all forms of tobacco smoking
Advice against alcohol, especially among
smokers
Reduce exposure to carcinogens in and outside
workplace
Avoid unnecessary use of suspected
carcinogenic drugs
Prudent use of diagnostic X-Ray
Avoid exposure to sunlight , especially light –skinned
Use minimum dose of estrogen to achieve theraputic
effect
Avoid giving estrogen to pregnant women
Enhance against female promiscuity, and male
homosexuality
Encourage having a diet with low fat and
meat but high in fruit , vegetables ,and fibers
Advice against obesity
Advice for early first full term pregnancy
CXR, and sputum cytology for CA-Lung: not
beneficial
Urinary cytology for CA-UB: not encouraging
results
Oral cytology for oral CA: Non-conclusive results
Barium meal for CA-stomach: Increased survival in
screened but not in general population
Testicular self-exam CA-testes: Not effective
Digital rectal exam for CA-rectum, and prostate:
Non-conclusive
BSE and mammography for CA breast : VERY
EFFECTIVE
Pap smear for CA cervix: VERY EFFECTIVE