It is well accepted that estradiol (E2) plays an important role in the genesis and evolution of breast cancer. Quantitative evaluation indicates that in human breast tumor, estrone sulfate (E1S) 'via sulfatase' is a much more likely precursor for E2 than is androstenedione 'via aromatase'. In previous studies, it was demonstrated that in isolated MCF-7 and T-47D breast cancer cell lines, estradiol can block estrone sulfatase activity. In the present study, the effect of E2 was explored using total normal and cancerous breast tissues. This study was carried out with post-menopausal patients with breast cancer. None of the patients had a history of endocrine, metabolic or hepatic diseases or had received treatment in the previous 2 months. Each patient received local anaesthetic (lidocaine 1%) and two regions of the mammary tissue were selected: (A) the tumoral tissue and (B) the distant zone (glandular tissue) which was considered as normal. Samples were placed in liquid nitrogen and stored at -80 degrees C until enzyme activity analysis. Breast cancer histotypes were ductal and post-menopausal stages were T2. Homogenates of tumoral or normal breast tissues (45-75 mg) were incubated in 20 mM Tris-HCl, pH 7.2 with physiological concentrations of [3H]-E1S (5 x 10(-9)M) alone or in the presence of E2 (5 x 10(-5) to 5 x 10(-7) M) during 30 min or 3 h. E1S, E1 and E2 were characterized by thin layer chromatography and quantified using the corresponding standard. The sulfatase activity is significantly more intense with the breast cancer tissue than normal tissue, since the concentration of E1 was 3.20 +/- 0.15 and 0.42 +/- 0.07 pmol/mg protein, respectively after 30 min incubation. The values were 27.8 +/- 1.8 and 3.5 +/- 0.21 pmol/mg protein, respectively after 3 h incubation. Estradiol at the concentration of 5 x 10(-7) M inhibits this conversion by 33% and 31% in cancerous and normal breast tissues, respectively and by 53% and 88% at the concentration of 5 x 10(-5) M after 30 min incubation. The values were 24% and 18% for 5 x 10(-7) M and 49% and 42% for 5 x 10(-5) M, respectively after 3h incubation. It was observed that [3H]-E1S is only converted to [3H]-E1 and not to [3H]-E2 in normal or cancerous breast tissues, which suggests a low or no 17beta-hydroxysteroid dehydrogenase (17beta-HSD) Type 1 reductive activity in these experimental conditions. In conclusion, estradiol is a strong anti-sulfatase agent in cancerous and normal breast tissues. This data can open attractive perspectives in clinical trials using this hormone.