Oestriol in human breast tumours

The role of oestriol in blocking the accumulation of oestradiol-17β by human breast tumours was investigated in patients with primary breast cancer. It was observed that oestriol is accumulated and retained by these tumours. However, pre-treatment of patients with 0.5 mg of the compound every 4 h for one and 3 days prior to mastectomy failed to reduce the accumulation of oestradiol indicating that, clinically oestriol may not be effective in inhibiting the action of oestradiol. The significance of the finding is discussed.