The isoflavones in soy are likely to contribute to the historically low incidence of breast cancer among Asian women that consume traditional diets. A possible role of isoflavones in controlling the expression of cyclooxygenase-2 (Cox-2) has not previously been explored. In this study, the ability of the isoflavone, genistein, to regulate the expression of Cox-2 in breast cancer cells was evaluated.

The effects of genistein and NS-398, a Cox-2 inhibitor, were examined on the expression of Cox-2 at the mRNA level using the MDA-MB 231, and MCF-7 breast cancer cell-lines.

In the MCF-7 cells, the Cox-2 mRNA could not be detected using RT-PCR. In the MDA-MB-231 cells, NS-398 and genistein were found to inhibit the Cox-2 mRNA expressions by 50 and 35~40%, respectively.

These studies suggest that dietary isoflavonoids may contribute to the prevention or inhibition of breast cancer by inhibiting the Cox-2 expression.