Background: We investigated the effect of Pap smear screening on the incidence of invasive cancer of the cervix in the Western Cape, South Africa where screening is limited.
Methods: Data were derived from a case-control study of the association of hormonal contraceptives and invasive cervical cancer. Incident cases (n = 524) of invasive cervical cancer who presented at two tertiary hospitals and controls (n = 1540) series matched for age, race, and place of residence were interviewed. Information on a wide range of variables was collected including whether the women had previously had a Pap smear taken and the number and timing of smears. Odds ratios (OR) and 95% CI were calculated using multiple logistic regression.
Results: The OR of cervical cancer was reduced among women who had ever had a smear (OR = 0.3, 95% CI: 0.3-0.4). The OR declined with increasing number of smears to 0.2 for >/=>3 smears (trend P = 0.0003). Among women who had a smear <5 years previously the OR was 0.3, but even if the smear was taken >/=15 years previously the women remained at reduced risk (OR = 0.5).
Conclusion: The data suggest that even limited Pap smear screening reduces the risk of cervical cancer. Should a screening programme be successfully implemented, the incidence of cervical cancer might be reduced by as much as 70%.