highly significantP < 0.001
Inconsistent results had been published on the relationship between plasma oestradiol levels and breast cancer risk, but this overview analysis of nine studies revealed a highly significant relationship (Fig. 1 ) in which there was an overall increase in relative risk of 1.29 (95% confidence interval, 1.15–1.44; P < 0.001) for every doubling of oestradiol concentration.