How to assess the effectiveness of a screening test for Cancer of the uterine cervix ?? Where is the evidence??

Organized cytology based screening programmes and the availability of accessible and good quality diagnosis and treatment facilities. Each screening test has its own strengths and limitations. Precancerous lesions are mostly asymptomatic. Limited sensitivity of conventional pap cytology ranging between 30 % and 87% . This is an area of major concern as high false negative rates results in premalignant or malignant cells being misdiagnosed as normal.

India alone accounts for one fourth of the global cervix cancer burden. Cancer of the uterine cervix is the second most common cancer among women globally. An estimated 550,700 new cases and 286, 823 deaths due to cervix cancer are estimated to have occurred in the year 2010 . More than 85 % cases and 885 deaths from cervix cancer occur in developing countries where women often in developing countries where women often lack access to cervical cancer screening and treatment.  .

This large scale morbidity and mortality is in warranted for two important reasons. Firstly the disease develops slowly after initial infection with the human papilloma virus and secondly unlike most other cancers it is preventable when precursor lesions are detected and treated. Women often do not experience any symptoms until the disease has advanced . Hence detection of cervix pre cancers and early stage cancers is  possible only through screening . The morbidity and mortality due  to cervix cancer declined dramatically in high income countries after introduction of organized cytology based screening programmes and the availability of accessible and good quality diagnosis and treatment facilities. In contrast even today millions of women in the developing countries are never screened for cervical cancer in their entire life time ; This is dues to lack of knowledge inaccessibility and poor quality of cervical cancer prevention and control services.

Several tests have been developed to screen women for cervix pre cancers and cancers . Each screening test has its own strengths and limitations. The same modality for cervix cancer control whether it is A) cytology visual based screening B) HPV DNA testing or C) HPV vaccination will never meet the demands of populations throughout the world .In the underserved populations factors such as low cost fewer visits for screening are vital. The choice of the test will depend on its technical performance cost effectiveness the available resources and the socio cultural settings in which it is to be used the various cervix cancer screening tests are described here.

Different Cervix cancer screening methods

A)Cytology—Based  screening.

A)Conventional cytology based screening with Pap smear test developed by George Papanicolaou has been the mainstay of cervical cancer prevention worldwide since the 1950s . Pap test has been exceptional to be accepted in a screening programme without its efficacy being tested with rigorous randomized controlled trials. However now there is convincing evidence about the benefits of cytology screening from many developed countries that introduced Pap test several decades ago. These countries are witnessing reduction in the incidence and death rates from cervix by over 50 % by screening with Pap test.

Cytology based screening programmes can be implemented effectively only if infrastructure and laboratory quality assurance requirements are consistently met.

Various studies have demonstrated limited sensitivity of conventional pap cytology ranging between 30 % and 87% . This is an area of major concern as high false negative rates results in premalignant or malignant cells being misdiagnosed as normal .Consequently the test needs to be repeated at frequent intervals to achieve programmatic effectiveness pap test has repeatedly demonstrated good specificity ranging from 86% to 100% .