CASE-CONTROL STUDY OF RISK-FACTORS FOR CERVICAL SQUAMOUS-CELL NEOPLASIA IN DENMARK .3. ROLE OF ORAL-CONTRACEPTIVE USE

The role of oral contraceptive (OC) use in relation to the risk of cer vical neoplasia (squamous cell) was investigated in a population-based case-control study in Denmark of 586 women with histologically verifi ed cervical carcinoma in situ (CIS), 59 women with invasive cervical c ancer from Copenhagen, and 614 controls drawn at random from the femal e population in the study area. Ever use of OCs was associated with an increased crude risk for carcinoma in situ (relative risk [RR] = 1.8, 95 percent confidence interval [CI] = 1.3-2.5). The crude risk in rel ation to invasive carcinoma was 1.6 (CI = 0.7-3.5). After adjustment f or potential confounders (excluding human papillomavirus), the risks w ere marginally increased, but not statistically significant (CIS: RR = 1.4, CI = 0.9-21: invasive: RR = 1.3, CI = 0.5-3.3). The risk increas ed with duration of use; compared with never users, the adjusted RR fo r carcinoma in situ was 1.9 (CI = 1.1-3.1) for women who had used OCs for six to nine years, and 1.7 (CI = 1.0-2.7) for women who used OCs f or 10 years or more. This was independent of years since last use sinc e both recent and non-recent long-term users were at an increased risk . This trend in risk with duration did not apply to the same extent to invasive lesions. The observation that the risks related to OC use we re found both in women who had ever had a Pap smear and in women who h ad never been screened previously may speak against detection bias as an important factor.