Patient Safety and Quality

Study provides estimates of cervical cancers that may be missed by extending screening time after consecutive negative Pap smears

Clinical recommendations currently encourage women to get Pap tests to screen for cervical cancer every 3 years, rather than annually, after three prior, consecutive negative tests. Yet many clinicians still perform annual Pap tests, perhaps due to perceptions that the increased risks associated with longer intervals are too great. A new study, supported in part by the Agency for Healthcare Research and Quality (HS07373), explored the risks of these intervals. Researchers calculated that in the first 18 months after the last negative screening Pap test in women with 3 or more prior negative tests, cancer incidence increased to an estimated 4 to 5 per 100,000 woman-years in each of the subsequent 2 years.

George F. Sawaya, M.D., of the University of California, San Francisco, and colleagues found 129 cases of cervical cancer were diagnosed within 3.5 years of one or more negative screening tests out of an estimated 6,802,641 woman-years of observation. After 3 or more negative tests, incidence per 100,000 woman-years grouped by time from the last negative screening test was: 1.43 0-18 months later, 4.24 19-30 months later, and 4.73 31-42 months later.

These estimations were based on a case-control study of cervical cancer screening efficacy among members of a prepaid health plan, who were diagnosed with cervical squamous cell cancer from 1983 to 1995. The cases were grouped by number of prior conventional Pap tests and by time from the last negative screening test to the diagnosis date. The cases were compared to matched controls (similarly screened women who did not develop cancer).

See "Cervical cancer after multiple negative cytologic tests in long-term members of a prepaid health plan," by Dr. Sawaya, Hai-Yen Sung, Ph.D., Walter Kinney, M.D., and others in the July 2005 Acta Cytologica 49(4), pp. 391-397.

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