Influence of non‐contraceptive exogenous and endogenous sex hormones on breast cancer risk in Denmark

Abstract

In order to evaluate the influence of sex hormones on breast cancer risk, a population‐based case‐control study was conducted in Denmark, including 1,486 cases diagnosed over a one‐year period. These were identified from the files of the nation‐wide clinical trial of the Danish Breast Cancer Cooperative Group and the Danish Cancer Registry. The control group was an age‐stratified random sample of 1,336 women from the general population. Data on risk factors were collected by self‐administered (mailed) questionnaires. The major findings included a trend (p = 0.001) toward decreasing risk with increasing age at menarche in pre‐menopausal women, trends toward increasing risk with continued menstrual cycles after the age of 50 in pre‐ and post‐menopausal women (p‐values of 0.01 and 0.002 respectively), and a trend (p = 0.002) toward increasing risk with increasing duration of non‐contraceptive sex hormone usage in post‐menopausal women. Information on brand names made it possible to examine types of hormones used, which showed an RR of 1.36 (95% CI 0.98–1.87) for sequential therapy with oestrogen and progestagen and RR = 2.31 (95% CI 1.37–3.88) for combined oestrogen‐androgen treatment. These results should be interpreted with caution, however, needing verification from other studies. No significant association was observed between breast cancer and self‐reported height and weight.