Another Look at the Pill and Breast Cancer

Abstract

This article presents a critical review of the contradictory findings of studies on the link between oral contraceptive (OC) use and breast cancer risk. The most recent of these studies, a large case-control study conducted in the US (the CASH study), found no change in the risk of breast cancer in OC users up to 45 years of age. This finding contrasts with Pike et al's conclusion that longterm use of OCs at a young age is associated with a substantial increase in breast cancer risk up to age 37 years. Further conclusions must await more epidemiologic investigation, mainly case-control studies. It is possible that a latent period is involved. It may be, for example, that 4 or more years of OC use before 25 years of age multiplies the risk of breast cancer by 3, but only after 10 years. If this is the case, the overall results of all epidemiologic studies that include young cases of breast cancer will underestimate any real effect of the longterm risk of early OC use. The precision and accuracy of such studies will improve steadily throughout the 1980s as the proportion of cases of breast cancer under the age of 45 years attributable to OC use increases. Moreover, there is some evidence that OC use among young women in the US lags 5 years behind that in the UK. The observation in the CASH study of risk only among the 20-24-year age group is not consistent unless longterm use among the young is such a recent practice that women over 25 years of age were not commonly exposed. In the future, investigators should specifically explore and report on the estimated effects associated with early longterm use of OCs, categorized by the interval between exposure and diagnosis of breast cancer. Finally, it is hoped that considerations of the effect of particular estrogens and progestagens at particular times of a woman's life will be made. Such evidence has potential for the prevention of breast cancer as well as for safe contraception.