Screening for cervical cancer

Screening for cervical lesions 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 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/ 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 2 nd smear if some women still have not had a 1 st 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 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