Breast cancer and oral contraceptives -- the evidence so far [editorial]

A recent report found a small increase in the risk of breast cancer among women who had recently used combined oral contraceptives (OC) but no increase for past users. Another report found a small increase in the risk of breast cancer among recent users of the progestogen-only OC but a significant decrease in risk for women who first used this OC 10 or more years ago. These studies join other studies that indicate that recency of use is the key determinant of breast cancer risk. The Collaborative Group on Hormonal Factors in Breast Cancer used 90% of the data available on this topic at the time. It concluded that OC users face a small but definite increase in the risk of breast cancer when compared to never users and that after discontinuation the increase falls and by 10 years after discontinuation past users no longer face an increased risk. This group also found that recent combined OC users faced a significant increased risk of localized breast cancer (relative risk [RR] = 1.21). This risk remained somewhat higher 5-9 years (RR = 1.07) and 10 or more years (RR = 1.04) after discontinuation. On the other hand the increased risk of cancer that spreads beyond the breast among recent OC users was minimal (RR = 1.09) but declined significantly in past users (RR= 0.96 for 5-9 years since first use and 0.93 for >or= 10 years). In fact past OC users had a lower risk of cancer spreading beyond the breast than never users. Some people have interpreted these findings to mean that OC users are more likely to detect breast cancer at an earlier stage. Yet recent OC users are no more likely to have had a mammogram than never users. Perhaps hormonal contraceptives or a combination of factors have a biologic effect on breast tissue. If these findings are confirmed they could have important public health consequences. Further research is needed.