Cancer epidemiology,
risk factors and prevention
Epidemiology
The study of the distribution,
frequency and determinants of health problems and diseases in human populations
to obtain, interpret and use health information to promote health and reduce disease
Crude death rate
Number of deaths per 1 000 of the
population per year
CDR = total
deaths in one year
mid
year population
Crude death rate per cause
Number of deaths from a particular
cause per 1 000 or per 100 000 of the population
CDR (per cause) = total deaths per cause per year
mid
year population
Standardised Mortality Ratio
The SMR is calculated by working out
an expected number of deaths in a given population from national figures and
comparing the expected death rate with the actual death rate. The national rate
is described a 100. SMR accounts for variations in age and sex in a population
profile so populations may be legitimately compared.
Incidence
Number of new cases/events/episodes
per year
A good indicator of increase or
decrease in a condition
Prevalence
Total number of existing cases at one
point in time
Prevalence = incidence x average
duration of the condition
Acute disease - high
incidence low prevalence
Chronic disease - low
incidence high prevalence
Morbidity
Mortality
Most common cancers, (1988 date)
Male Female
lung breast
skin skin
prostate lung
bladder colon
colon ovary
stomach rectum
rectum stomach
non- Hodgkin cervix
pancreas uterus
oesophagus bladder
Principles of aetiology
Causes
Radiation
Chemical carcinogens
Occupation
Virus (Epstein Barr)
Diet
Disorder of immunity
Heredity
Hormones
Environmental factors
Immunosupression
Age
Endogenous oncogenes
Exogenous oncogenes
Free radical theory
Multi-step theory of neoplasia
Initiator - causes a
change in the genetic material, must be applied first
Promoter - applied at regular intervals
over time removal of the promoter
in pre - malignant tissue can remove or reduce risk
Complete carcinogens - initiators and promoters
Incomplete carcinogens - initiators
or promoters
Genetics
Clusters of various primary sites
sometimes occur in families often effecting members below the age of 45 years
Mutations can cause cancer
Oncogenes
Autosomal dominant
Retinoblastoma
Familial polyposis
Cancers caused by gene mutations
Colon cancer
Osteosarcoma
Small cell
Testicular
Principles of prevention
5 a day
ACE vitamins
Selenium
Flavinoids
Less fat and meat
Cancer warning signs
Aim is early recognition of the
condition
* Change
in bowel habit
* Sore
which does not heal
* Unusual
bleeding or discharge
* Thickening
or lump somewhere, (self examination)
* Difficulty
in ingestion
* Changes
in a wart or mole
* Nagging
cough or hoarseness
Health of the Nation headings
Sketch the local picture
Seek local views
Develop local alliances
Assess available interventions
Identify research and development
needs
Agree local targets
Agree strategies for achieving local
targets
Develop skills and resources
Monitoring, evaluation and
dissemination
Screening
Must be :-
Cheap
Be acceptable to all social groups
Have a good discriminatory index from
benign lesions
Result in improved prognosis
Health Education
Health promotion
Lung
Most common primary malignant
condition in the West, (UK about 34 000 per year).
Very uncommon under 35 years common
over 65 years
Risk factors
Smoking - 80% (26 000 deaths per year)
of cases associated with active smoking, several hundred deaths associated with
passive smoking
Radon gas (5% of cases) potentiated by
smoking by 10 times
Radioactive minerals, asbestos,
nickel, chromium, coal gas, metallic iron and iron oxides
Asbestos potentiated by smoking by 40
times
Living in a city
Increased risk from dietary
cholesterol, animal fat and saturated fat
Protective factors - beta- carotene
and other factors in vegetables
Screening
No useful test exists
Breast
Incidence has increased over past 30
years
Most common malignancy in women in the
West, (22 000 per year in the UK with over 13 000 deaths)
Countries with traditionally low rates
are experiencing increasing rates
Most women over 50 years of age
Risk factors
Aetiology poorly understood
Most risk factors seem to operate
through hormonal mechanisms
Early onset of menstruation
Late menopause
Age at first full term pregnancy
(older mothers at greater risk)
Obesity
Excessive alcohol consumption
Benign breast disease
Not breast feeding
Genetics
Oral contraception
More common in socio-economic class I
and II
Screening option
Teach breast awareness
Professional examination in fibrotic
breasts
Mammography
Cervical
Most common presentation is early 60s
Some recent increase in younger women
Risk factors
Root cause unclear
Human papilloma virus
Lower socio-economic groups more at
risk
Age at first intercourse
Multiple partners or partners with
multiple partners
Smoking doubles the risk
Screening
Cervical cytology every 3 years
Skin
Malignant melanoma (MM)- aggressive
Non- Melatotic Skin Cancers (NMSC)-
mostly basal cell and squamous cell
Steady increases in incidence
Risk factors
NMSC
Chronic sun exposure
MM
Episodes of sunburn in childhood
Severe sunburn
More common nearer the equator (10 -
12 more common in whites)
Skin type - white skin which burns
easily and tans poorly
Screening
Teach importance of early reporting of
new growth or changes to moles and warts
Colorectal
Second most common malignancy in the
UK
Incidence increases with age average
diagnosis is 60 - 65 years
Risk factors
Eating meat and animal fat
Lack of fibre
Ulcerative colitis
Activation of proto-oncogenes
2 -3 times greater risk if first order
relatives are affected
Polyposis (20% of polyps > 2cm)
Screening
Genetic counselling in polyps
Faecal occult bloods, (reduces 13 year
mortality by 33%)
Single flexible sigmoidoscopy at 55
years, (for first or second degree relatives)
Oesophageal
Common in China, parts of Africa and
Iran
5 - 10 per 100 000 in the UK - 2.5% of
all malignant disease
Risk factors
More common in men
Heavy alcohol consumption
Smoking
Coeliac disease
Long standing reflux
Screening
None
Stomach
Common in Japan and China
Relatively uncommon in the USA
6th most common cancer in the UK
Incidence seems to be falling world-
wide
Incidence increased with age
More common in men
Risk factors
Helicobactor pylori
May spread in families
Alcohol, spices food, salt, pickles,
nitrates
Smoking
Blood group A
Pernicious anaemia
Gastric ulcers do not turn malignant
Screening
Japan - mass screening with mobile X
ray units
No useful test
Liver
Hepatocellular carcinoma is one of the
most common cancers world-wide
Risk factors
Carriers of HBV and HCV have a high
risk
In endemic HBV areas 90% of cases are
HBV positive
10% of patients who have had acute HBV
infection become chronic carriers
Associated with cirrhosis
Males affected more than females
Aflotoxins
Androgenic steroids
Association with oral contraception
Screening
No useful test known
Testicular
Commonest cancer of young men 15 - 35
1 - 2 % of all cancers in the UK
Risk factors
History of undescended testis
Screening
Teach testicular awareness
References
Health of the Nation, Cancers, Key areas handbook,
(1992) Dept of Health
Kumar P. Clark M. (1995) Clinical Medicine, (third ed.)
Bailliere Tindale, London
Bourke GJ. (1983) The Epidemiology of Cancer,
Croom Helm, Philadelphia
Hancock, (1996), Cancer care in the community,
Radcliffe Medical press, Oxford