To determine the sensitivity and specificity of the Pap smear, both a test threshold (i.e., the point at which the test will be considered to be “positive”) and a reference-standard threshold (i.e., the point at which the reference standard is considered to be “positive”) must be defined.In practice, ASCUS is often used as the test threshold, and CIN 1 is often used as the reference threshold.Reductions in cervical cancer incidence and mortality were proportional to the intensity of screening.[16,20] Mortality in the Canadian provinces was reduced most remarkably in British Columbia, which had screening rates two to five times those of the other provinces. Case-control studies have found that the risk of developing invasive cervical cancer is three to ten times higher in women who have not been screened.[22-25] Risk also increases with long duration following the last normal Pap test, or similarly, with decreasing frequency of screening.[26,27] Screening every 2 to 3 years, however, has not been found to increase significantly the risk of finding invasive cervical cancer above the risk expected with annual screening.[27,28] Ideally, determining the sensitivity and specificity of a screening test would involve a study that applies a “gold standard” test (such as colposcopy with appropriate biopsy) to all participants (whether the screening test results are positive or negative).Sensitivity (the percentage of “true-positive” cases that are detected by the screening test) and specificity (the percentage of "true-negative" cases that are negative by the screening test) could be calculated.Harms are also increased in younger women because they have a higher rate of false-positive results.Magnitude of Effect: Additional diagnostic procedures were performed in 50% of women undergoing regular Pap testing. The number with impaired fertility and pregnancy complications is unknown.From 2006 to 2015, the death rate decreased by 0.8% per year. This improvement has been attributed largely to screening with the Papanicolaou (Pap) test.
Both incidence and mortality from cervical cancer have sharply decreased in a number of large populations following the introduction of well-run screening programs.[16-19] In Iceland, the mortality rate declined by 80% for more than 20 years, and in Finland and Sweden by 50% and 34%, respectively.[16,20] Similar reductions have been observed in large populations in the United States and Canada.
A further categorization, the Bethesda system, is based on cytologic findings: atypical squamous cells of undetermined significance (ASCUS) or cannot rule out low-grade squamous intraepithelial lesions (LSILs), LSILs (consisting of cytologic atypia and CIN 1), and high-grade squamous intraepithelial lesions (HSILs), primarily CIN 2–3 plus carcinoma . The rate at which invasive cancer develops from CIN is usually slow, measured in years and perhaps decades. This long natural history provides the opportunity for screening to effectively detect this process during the preinvasive phase, thus allowing early treatment and cure.
Because many of these preinvasive lesions (especially LSILs) would have never progressed to invasive cancer,[5-7] screening also runs the risk of leading to treatment for women who do not need to be treated.
In the United States in 2018, it is estimated that 13,240 cases of invasive cervical cancer will be diagnosed and that 4,170 women will die of the disease. These rates have been improving steadily.
From 2005 to 2014, overall incidence rates stabilized.