Abstract

PIP: This article suggests that an improper definition of prior history of benign breast disease may be responsible for research results that show an increased risk of breast cancer among oral contraceptive (OC) users with such a history. It is maintained that women who developed fibrocystic breast disease in the 1960s-late 1970s despite longterm use of OCs were intrinsically at greater risk of breast cancer than nonusers who developed fibrocystic disease. Thus, it is improper in epidemiologic studies of OC use and the risk of breast cancer to define a prior history of fibrocystic disease as prior to the development of breast cancer or to corresponding reference ages of women without breast cancer. Rather, prior history should be defined as prior to the use of OCs. The article further analyzes the 3 major case-control studies of breast cancer that developed before 1978 that have suggested OC use increases the risk of breast cancer in women with a prior history of benign breast disease. In the 1st study, by Paffenbarger et al, the operational definition of prior history of benign breast disease appears to be prior to hospitalization for breast cancer. In the 2nd study, by Lees et al, a prior history was defined as prior to presentation at the clinic. In the 3rd study, by Brinton et al, a prior history of benign breast disease was defined as prior to the 1st screening. When stratification or adjustment for prior history of benign breast disease is restricted to disease that develops prior to any OC use, the epidemiologic studies fail to show that women with existing benign breast disease who initiate OC use alter their risk of developing breast cancer.