suitable study have increased. A number of the studies reviewed here were plagued with limitations that, at the very least, render these studies suboptimal. Future case-control studies should be carefully designed so as to avoid some of these pitfalls. More work is needed to address the possibility of recall bias, although it is hard to believe that reporting of long-term use is compromised enough to explain the recent emergence of positive findings. Validation of a reported history of oral contraceptive use through medical record review would be ideal, but is quite difficult in the United States or any country where people are mobile and do not have a centralized source of health care. Case-control or small validation studies conducted in health maintenance organizations, or studies in countries with national health care systems, both of which have lifelong medical records for study subjects, might be the best way to evaluate the question of misclassification of oral contraceptive use because of recall bias. Future case-control studies should be population based, achieve high levels of response, and be designed to minimize the likelihood of introducing bias.
The causes of the increase in breast cancer incidence should be investigated further, and the extent to which increased breast screening contributes to the increased incidence should be evaluated. In turn, for case-control studies, the degree to which increased screening of oral contraceptive users affects case identification needs to be evaluated.
In existing and future data, especially those studies with large enough numbers of subjects, more effort is needed to tease out the effects of long duration of exposure versus exposure at specific ages—as well as other patterns of use that may be associated with adverse or protective effects. In particular, the effect of use at an early age should be further evaluated to distinguish the timing of exposure from the longer duration of exposure that is associated with beginning use at an earlier age. Besides examining oral contraceptive use at young ages, there are unanswered questions concerning use during the perimenopausal years. The recent FDA decision to lift the recommended upper age limit for use of oral contraceptives will probably lead to increased use in the over-40 age group. The relationship between oral contraceptives and breast cancer risk also needs to be examined in other subgroups, such as women with a strong family history of breast cancer and women with previous benign breast disease, using data sets with sufficient numbers of subjects.
In conclusion, the current picture of the relationship between oral contraceptives and breast cancer is rather confusing. It is not clear whether we should be reassured or alarmed, or whether it is just too