Recently revised guidelines have suggested that the interval between cervical cancer screening tests might be lengthened to three years in women with previously normal Papanicolaou (Pap) smears and no increased risk factors for cervical cancer. This shift from the longstanding recommendation for annual Pap tests was caused by a lack of evidence that frequent screening in low-risk women provided any additional protection against cervical cancer. Sawaya and colleagues, with the Centers for Disease Control and Prevention (CDC), examined nationwide cervical cancer screening data to quantify the relative risks associated with less frequent screening.

The authors analyzed data from a somewhat higher risk population of low-income, underinsured women who received cervical cancer screening through a nationwide program administered by the CDC. Approximately one half of the participants were from minority groups, and more than one half were older than 45 years.A total of 1,174,727 screening tests were reviewed. The authors excluded 19,784 tests (1.7 percent) that had unsatisfactory technique or unclear cytology results. If Pap tests from any participants were performed more often than every nine months, they were considered likely to represent surveillance of a known abnormality rather than simple screening, and they were excluded. Cytology results were reported using the 1991 Bethesda System categories.

Biopsy-proven dysplasia occurred most frequently in women younger than 30 years. Cervical cancer was rare overall, and almost all cases of cancer occurred in women with no history of screening (0.02 to 0.06 percent incidence across age groups). No cases of invasive cervical cancer occurred in women who had at least three previously normal Pap tests. Using mathematical models, the authors calculated the extra risk of cervical cancer that would occur if women with three consecutive normal screening tests extended the interval between Pap tests to three years, instead of one year. The increased incidence of cancer was approximately three cases per 100,000 women between 30 and 64 years of age. For comparison, the authors noted that this increase was about even with the risk of breast cancer among men 45 to 64 years of age.

The authors conclude that annual cervical cancer screening in women with three previously normal Pap smears provides a negligible benefit, and that the screening interval may be extended safely to every three years in this low-risk group.

editor's note: Even in the higher risk population of low-income, underinsured women, cervical cancer occurred almost exclusively in patients with no previous Pap testing. To best reduce the suffering from cervical cancer, physicians need to direct their efforts toward reaching women who have never been screened, rather than repeat millions of annual Pap smears in low-risk patients who derive no benefit, yet endure some inconvenience and expense from frequent testing.—b.z.