Although cervical cancer mortality increases with age, the prevalence of CIN is highest among women in their 20s and 30s. Mortality is rare among women younger than 30 years; HSIL is rare among women older than 65 years who have been previously screened. About 70% of ASCUS and CIN 1 lesions regress within 6 years, while about 6% of CIN 1 lesions progress to CIN 3 or worse. In about 10% to 20% of women with CIN 3 lesions, the lesions progress to invasive cancer.[3,6,14]
Cervical cancer mortality is about 40% higher in black women younger than 65 years than in white women of the same age. Among women older than 65 years, cervical cancer mortality for black women is more than 150% higher than for white women. In either case, mortality is rare among women of any age who have regular screenings.
The Pap Test
The Pap test has never been examined in a randomized controlled trial. A large body of consistent observational data, however, supports its effectiveness in reducing mortality from cervical cancer. Both incidence and mortality from cervical cancer have sharply decreased in a number of large populations following the introduction of well-run screening programs.[15,16,17,18] In Iceland, the mortality rate declined by 80% for more than 20 years, and in Finland and Sweden by 50% and 34%, respectively.[15,19] Similar reductions have been observed in large populations in the United States and Canada. Reductions in cervical cancer incidence and mortality were proportional to the intensity of screening.[15,19] 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 greater in women who have not been screened.[21,22,23,24] Risk also increases with long duration following the last normal Pap test, or similarly, with decreasing frequency of screening.[25,26] 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.[26,27]