Breast cancer and combined oral contraceptives: an Italian case-control study

The risk of breast cancer in relation to use of oral contraceptives was evaluated using data from a hospital-based case-control study from Northern Italy on 1517 cases below age 60 and 1351 controls admitted for acute diseases unrelated to any of the known or potential risk factors for breast cancer. The multivariate relative risk for ever vs. never users was 1.3 (95% confidence interval = 1.0-1.7). However, the risk was not related to duration of use: indeed the highest risk was observed among short-term users (less than 2 years), and the point estimate was 0.9 among users for 5 years or more. The elevated risk among short-term users, if not due to residual confounding or selection mechanisms, is probably explainable in terms of recall bias (i.e. more careful report of short or very short use by cases). No definite pattern was observed in relation to latency or recency of use, and the point estimates were 0.8 for women who had ever used the pill before age 25 and 0.8 for those who had ever used the pill before first full-term pregnancy. Thus, the study presents further reassuring information on the oral contraceptive/breast cancer debate. Its major limitation lies in the low prevalence of oral contraceptive users in Italy, with a consequently reduced statistical power, although, with the number of cases involved, it was possible to exclude a relative risk of 1.4 for long-term use or for ever use before first birth.