Cervical cancer develops from slowly progressing intraepithelial lesions. If early changes in cervical cells are detected through screening programmes, cervical cancer is preventable.
Countries with effective screening programmes have a significantly reduced burden of cervical cancer, in some instances by as much as 80% over the last four decades. However, if undetected until late in its clinical course, it has a high death rate.
Screening programmes involve the testing of an asymptomatic “health” population. The primary goal of cervical screening is to detect pre-invasive cancers and prevent death from cervical cancer by treating pre-cancerous lesions. There are a number of methods used to screen for cervical cancer precursors.
The frequently used Pap test has good specificity but relatively poor sensitivity. A Pap test collects cells from the cervix to test for any abnormalities.
The Pap test has been successful in decreasing cervical cancer death rates in industrialized countries. Pap tests, do not detect all pre-cancerous lesions, and are extremely labour intensive, complex and tedious. They are not effective in low resource or developing health economies due to lack of infrastructure and lack of highly trained personnel to read the smear.
Visual inspection methods are often used in low-resource settings as they are inexpensive and provide an immediate result. However, they are relatively non-specific and have low sensitivity.
Liquid-based cytology (e.g. ThinPrep) is a variation on the conventional Pap test. Recent research has shown that liquid-based cytology does not show any advantage over conventional Pap tests in terms of sensitivity and specificity.
HPV DNA TESTING
DNA Testing for HPV is a more recent screening method. Studies show it is more effective at early detection than a traditional Pap test, as it is more accurate and can detect cell abnormalities earlier on.
There is a strong association between persistent infection with high-risk oncogenic types of HPV, the development of cervical cancer precursor lesions and the subsequent development of cervical cancer. Therefore, development of cervical cancer is associated with persistent infection with oncogenic types of HPV.
The testing of DNA for HPV may be useful in the triage of low-grade cervical changes, follow-up of non-confirmed, possible high-grade changes, post-colposcopy follow-up of CIN 2-3 and clarifying indeterminate histology.
Although HPV DNA testing has started to be approved for screening in developed countries, it is a quite expensive process that will not be affordable for population based screening in developing countries. Furthermore, like PAP and Liquid Based Cytology, HPV tests need an infrastructure of laboratory facilities which are lacking in developing countries.
Over 41% of countries globally have the HPV Vaccines in their National Immunisation Programme, however, availability and coverage is limited throughout many developing countries. While vaccination is far less costly than diagnostic procedures and treatment, the currently available vaccines only cover the types of HPV that cause 70% of cervical cancer cases.
Although vaccines are effective in the prevention of persistent HPV infection, it is essential that women continue to undergo cervical cancer screening because:
- Vaccines are only effective for women who have not had sexual contact. Guidelines in many countries do not vaccinate women over 13 years of age.
- The duration of the effectiveness of vaccines is unknown.
- The opportunistic rise in prevalence of previously low incident oncogenic HPV types cannot be predicted.