BACKGROUND

Although the effectiveness of cervical cancer screening has been firmly established in reproductive-age women, its usefulness in older women is unclear. We sought to evaluate the efficacy of cervical cancer screening in older women.

METHODS

We conducted a case-control study within two integrated health care systems in the northwestern United States. Cases (n = 69) were women aged 55-79 years who were diagnosed with invasive cervical cancer during 1980-1999. Controls (n = 208) were women with an intact uterus and no diagnosis of cervical cancer, but otherwise similar to cases in terms of age and length of enrollment in the health plan. We reviewed medical records to ascertain screening history during the 7 years prior to reference date.

RESULTS

Compared to cases, controls were more likely to have received a Pap test. After adjustment for age and current smoking status, screening prior to an estimated 1-year duration of the occult invasive phase of cervical cancer was associated with a substantial reduction in risk [odds ratio (OR) 0.23; 95% CI 0.11-0.44]. Similar results were obtained using different estimates of the duration of the occult invasive phase. 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 5-7 years.

CONCLUSIONS

Cervical cancer screening by means of cytology is highly efficacious in older women. Our findings also suggest that five-yearly screening is approximately as efficacious as more frequent screening.