Oral Contraceptives in Relation to Breast Cancer

Even though many studies have examined the relationship between oral contraceptive (OC) use and breast cancer risk, we still do not know whether OCs increase the risk of breast cancer. Evidence suggests that longterm OC use may possible increase the risk of breast cancer in women under 45 years old. The risk may be increased in women who use OCs after age 40. Almost no data suggest an increased of breast cancer in women who first used OCs at a late age or for spacing pregnancies. Epidemiologist, clinicians, and basic scientists need to join together to gain more insight into this relationship. Research needs to develop in vitro breast tissue systems to investigate growth, differentiation, and transformation effects of hormonal factors and methods to classify OC formulations in such a way as to ascertain their effect on breast tissue. It also needs to continue to study the relationship between hormonal exposures and local growth factors and oncogenes. Future case control studies should confirm to the following criteria: be population based, include many women who were first exposed to OCs while still young, able to generate a high response, and designed to reduce the probability of bias. Researchers also need to compare the distribution of OC use and other breast cancer risk factors of both participants of case control studies and nonparticipants to these studies' results. Researchers must look at ways to increase study participation, e.g., financial incentives and public education. Studies in health maintenance organizations or countries with national health care systems, which tend to have longterm medical records, would address recall bias. Researchers need to continue following women who first used and continue to use OCs at an early age to ascertain the effects of OCs in the perimenopausal years. Other groups include women with a strong family history of breast cancer, with previous benign breast disease, or with a history of induced abortion.