Cervical Cancer Screening Efficacy in Older Women

Abstract

Abstract Although the effectiveness of cervical cancer screening, by means of the Pap smear, has been firmly established in reproductive-age women, the usefulness of cytologic screening in older women is unclear. We sought to assess the degree to which such screening in older women can reduce the incidence of cervical cancer. We conducted a case-control study to evaluate the efficacy of cervical cancer screening in older women enrolled in one of two large health maintenance organizations in the northwestern United States. Cases (n = 69) consisted of those women, 55 to 79 years of age, who were diagnosed with invasive cervical cancer during 1980 to 1999 as enumerated by regional cancer registries. Controls (n = 208) were women sampled from among enrollees who had not previously had a hysterectomy and were similar to cases in terms of age and length of enrollment in the health plan. We reviewed medical records to ascertain demographic, reproductive, and cervical screening history information during the 7 years before the reference date. Only tests which occurred during the presumed detectable preinvasive phase (DPP) of the disease, when screening could be beneficial, were considered and we evaluated results for a series of plausible estimates of this interval. Compared to cases, controls were more likely to have had a Pap test during the DPP, regardless of the estimate used. After adjustment for age and current smoking status, screening was associated with a substantial reduction in the risk of invasive cervical cancer (DPP = 72 months: OR, 0.23; 95% CI, 0.11–0.44). We observed only small differences in the odds ratio across the various estimates of the DPP that were employed. Analysis of the relative incidence of invasive cervical cancer in relation to the time following a negative screening test suggested a large reduction during the first year (OR, 0.09; 95% CI, 0.03–0.24). The incidence remained low for several years thereafter, returning to the incidence among unscreened women after 5 to 7 years. Cervical cancer screening is highly efficacious in older women. This needs to be explicitly considered in weighing the benefits and costs of such screening beyond the reproductive years.