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Effect of breast cyst fluid on oestrone sulphatase activity in MCF-7 breast cancer cells.

Breast cyst fluid is a rich source of growth factors and sex hormones but the pathophysiology of cystic breast disease is largely unknown. In this study the net effects of breast cyst fluid on growth of, and oestrone sulphatase activity (oestrone sulphate --> oestrone) in the hormone-dependent MCF-7 and hormone-independent MDA-MB-231 breast cancer cell lines were assessed. Using a final breast cyst fluid dilution of 16.7% (v/v) MCF-7 cell growth was significantly inhibited by 7 of 21 samples (16% - 54%) while MDA-MB-231 cell growth was significantly inhibited by 17 of 20 samples (15% - 45%). Oestrone sulphatase activity was significantly inhibited in the MCF-7 cell line by 19 of 21 samples (22% - 81%) while significant stimulation of oestrone sulphatase activity was observed in MDA-MB-231 cells in 11 of 20 samples (17% - 149%). The presence of endogenous substances in breast cyst fluid which inhibit oestrone sulphatase activity in the MCF-7 cell line is exciting because of the therapeutic potential of oestrone sulphatase inhibition in hormone-dependent breast cancers.