ORAL-CONTRACEPTIVES AND BREAST-CANCER IN NORTHERN ITALY - FINAL REPORT FROM A CASE-CONTROL STUDY

To assess the relation between oral contraceptive (OC) use and breast cancer, we analysed data from a case-control study conducted in Northe rn Italy between 1983 and 1991 on 2,309 cases below age 60 and 1,928 c ontrols admitted to hospital for acute diseases unrelated to OC use an d to any of the known or potential risk factors for breast cancer. OC use was reported by 16% of cases and 14% of controls. The multivariate relative risk (RR) for ever vs never use of combination OC was 1.2 (9 5% confidence interval (CI) 1.0-1.4). However, there was no trend in r isk with duration. The RR was elevated for very short use, but decline d to 0.8 (95% CI = 0.5-1.0) for five or more years' use. No noteworthy relationship was found for other major measures of OC use, although R R estimates were above unity for women who had stopped use less than 5 years before (RR = 1.5, 95% CI = 1.1-2.0), started use less than 10 y ears before (RR = 1.3, 95% CI = 1.0-1.9), started when 25 or more year s old (RR = 1.4, 95% CI = 1.1-1.7), or after first birth (RR = 1.2, 95 % CI = 1.0-1.5). No interaction was observed between OC use and family history of breast cancer, parity and age at first birth. A separate a nalysis of 373 cases and 456 control below age 40 showed no associatio n with ever use (RR = 0.9, 95% CI = 0.6-1.2).