Transcript Screening for cervical cancer

Screening for cervical cancer
Screening for cervical lesions
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Common disease
Cancer is preventable
Screening is easy
MUST BE PERFORMED
Why screening?
• To detect presence of disease in an
asymptomatic population
• This will allow interventions and we may
TREAT / stop progression / prevent worse
disease to develop
• For screening to be effective the disease
must be Common, the Population must be
covered, and the Test must be good
A good screening test
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Safe, acceptable to the patient
Simple and easy to perform, repeatable
Of acceptably low cost
Sensitive (correctly identify those with the
abnormality)
• Specific (correctly identify the
nondiseased)
• High predictive value (sens + spec)
Conventional screening for cervical
cancer and its precursors
• Cervical cytology is widely used
• The taking of a scraping or smear from the
cervical surface epithelium for cytological
analysis
• Objective: to detect those women with
asymptomatic abnormalities, to detect
precursors, to treat those and to prevent
the occurrence of cervical cancer
Cytology
• Nickname: Papsmear (Dr Georges
Papanicoloauo 1940’s: staining technique)
• Criteria: safe, acceptable, easy,
reasonably affordable BUT low sensitivity
and low specificity
• If total population is screened repeatedly:
can decrease the incidence of CaCx within
20y from 20 down to 6/100 000 women
new cases per year
Coverage
• WHO: all women in a country should get at
least one smear in her lifetime; nobody
should get a 2nd smear if some women still
have not had a 1st smear
• SA: State policy: 3 smears / women /
lifetime (ages +/- 30,40,50) (problem in
areas with high HIV)
• SA: private: a commodity: +/- annual
Ideal system?
• All sexually active women should be
screened within the first year of onset of
sexual activity, then annually until 3 normal
smears have been obtained, then 3yearly
• Continue until at least 65-70 y of age
Typical smear results: Bethesda
system
• Normal +/- infectious changes
• ASC (infectious or atypia)
• SIL: squamous intraepithelial lesions
– Low grade
– High grade
• AGUS
• Adenocarcinoma in situ
• Invasive squamous- or adenocarcinoma
Reasons for false positive smears
• Abnormal smear but no disease:
– Atrophy
– Infections esp. trichomoniasis
– Folic acid deficiency
– Previous radiotherapy
– Laboratory errors
Reasons for false negative smears
• Normal smear but missed diagnosis!!
– Smear not taken from transformation zone
– Too few cells on slide
– Deficient fixation of smear
– Slide covered with blood or pus
– Laboratory errors
Alternatives to cytology
• 1 Visual screening by inspection
– Acetic acid 3% solution applied to cervix
– Observe for white change in epithelium
(acetowhite)
– Can also detect existing cancers
– Low sensitivity, specificity, predictive value
– Downstaging possible
– A real developing world alternative
Alternatives (2)
• HPV screening (a cost issue…)
– Can test for high risk HPV types (PCR test)
– Current usage: below 30y: prevalence of HPV
infection too high to make conclusions
– After age 30y: if HR HPV +: refer for cytology
– Advantage: can do HPV in young person with
ASC: if also HPV +, rather treat
– Ultimately: when more affordable: if both HPV
and cytology are -, need to screen again
rarely