Duration of relative protection of screening for cervical cancer

The reduction in cervical cancer among women with at least one previous negative Pap smear can be assessed in terms of the time elapsed since the last smear was taken. One indicator of the utility of screening is the duration of relative protection, commonly calculated as the inverse of the disease odds ratio. Most investigations of the extent of relative protection provided by Pap testing have relied on data from centrally organized screening programs or case-control studies. For geographic areas without mass screening programs or tumor registries, reliance on subject recall of Pap tests is required. We conducted a case-control investigation of cervical cancer and interviewed 153 Maryland women with invasive disease and two control groups: 153 case-nominated controls and 392 randomly selected controls. The duration of relative protection of screening for disease was 4-6 years for both control groups [relative protection (RP) = 4.30, 95% confidence interval (CI) = 1.5-12.7 for neighborhood controls, RP = 3.63, 95% CI = 1.4-9.6 for random controls]. These findings held after adjusting for education, ever treated for a sexually transmitted disease, smoking, age at menarche and at first sexual intercourse, number of pregnancies, lifetime contraceptive use, and utilization of obstetrician-gynecologist services; the RPs increased upon adjustment. However, there was a decline in the RP with increased duration. Our findings are directly comparable to reports where smears have been verified, suggesting that self-reports of previous tests may be reliable as a method to evaluate the utility of screening.