Oral contraceptives and breast cancer. A review

Case-control and cohort studies published between 1977 and 1988 were reviewed with the purpose to evaluate the relationship between use of oral contraceptives (OC-use) and breast cancer risk, tumour biology and tumour prognosis with special emphasis on early OC-use. The risk of breast cancer was assessed in 30 case-referent studies and 5 cohort studies, and the prognosis of breast cancer had been studied in 9 reports. Definition of OC-use, prevalence of OC-use, latency time between start of OC-use and tumour diagnosis, case identification and choice of referents, study size, study quality were assessed. The outcome of the studies is presented. From the results of the analyses the author concludes that there is no overall risk for breast cancer among OC-users. However, with the emphasis on early OC-use, consistent results seem to emerge showing an increased risk of premenopausal breast cancer, when the possible bias of different latency times is taken into account. Also results on breast cancer incidence in early exposed age groups, tumour biology and prognosis in early OC-users with breast cancer support a genuine risk relationship. The effects of different OC-brands and dose, and the risk of peri- and postmenopausal breast cancer after early OC-use can at present not be assessed.