Limited Pap screening associated with reduced risk of cervical cancer in South Africa.

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%.