Binding of oestradiol to blood proteins and aetiology of breast cancer.

A prospective study of 5,000 women has shown that, compared to controls, those who subsequently developed breast cancer had a higher proportion of their blood oestradiol in the non-protein-bound and albumin-bound fractions (the bio-available fraction) and a lower proportion in the sex-hormone-bound fraction. The increased proportion of bio-available oestradiol was partly due to a lower concentration of sex-hormone-binding globulin. Weight was excluded as a confounding factor.