Relationships between oestrogen-inducible proteins, oestradiol and electrolyte ratio in breast cyst fluid.

Women who have breast cysts with intracystic Na+/K+ < 3 may have a higher risk of developing breast cancer than women who have breast cysts with intracystic Na+/K+ > 3. In this study wide-ranging intracystic concentrations of cathepsin D and pS2 (oestrogen inducible proteins/polypeptides) as well as oestradiol were found. The concentrations of cathepsin D and oestradiol were significantly higher in the low electrolyte ratio cyst group than in the high electrolyte ratio cyst group. No significant difference was found between pS2 concentrations in the two groups. The significantly higher intracystic concentrations of cathepsin D, a mitogenic lysosomal endopeptidase and oestradiol in the low electrolyte ratio group may partly provide an explanation for the higher risk of breast cancer which has been observed in this group of women.