Survival in breast cancer and age at start of oral contraceptive usage

In general, findings in studies on oral contraceptives (OCs) and breast cancer have not indicated prognosis to be worse among users of OCs. In few studies, however, has age at the start of OC usage been considered as a prognostic factor. In the present study, prognosis in breast cancer is compared with OC usage, particularly with age at the start of OC usage, among 193 consecutive patients at the Department of Oncology, University Hospital, Lund. An earlier series of 193 breast cancer patients at Malmö General Hospital is included for comparisons. In the Lund series, five-year survival was 62% among women who started to use OCs before the age of 20.78% among those who started to use OCs between the ages of 20 and 25, and 86% among non-users and those who started to use OCs after the age of 25 (p = 0.009, test for homogeneity). Although age was found to be a prognostic factor in the Lund series (RR = 0.90, p = 0.001), this was not so in the earlier (older) Malmö series. The relationship with age differed significantly between the two series (p = 0.003), suggesting the apparent effect of age at diagnosis to be a cohort effect due to the introduction of OCs during the 'sixties. The age-specific relationship between survival and OC usage would seem to indicate the presence of a biological mechanism in which OCs may participate during precancerous and early stages of breast cancer.