[Estrogen-induced genes in breast cancer, and their medical importance]

The study of several human estrogen receptor positive breast cancer cell lines has allowed characterization of a number of estrogen-induced proteins (e.g. progesterone receptor, cathepsin D, pS2 and fibulin-1 in ovarian cell lines). In primary tumours, these markers have different prognostic significance for predicting whether the tumour will be hormone responsive (e.g. pS2, estrogen and progesterone receptors) or will develop metastasis (e.g. cathepsin D). Studies of estrogen-regulated genes should also lead to new therapeutic approaches for hormone-resistant cancers. The role of estrogens as mitogens stimulating the growth of breast and ovarian cancer cell lines is well established. By contrast, their action on metastasis appears more ambiguous. Breast cancer cells without estrogen receptor (ER) are generally less differentiated and more aggressive than those containing functional ER. Moreover, the reexpression of ER by transfection in ER-negative cell lines inhibit their metastatic and invasive potential. These results suggest a protective role of ER in tumor progression. Studies of the underlying mechanisms of this effect may open new therapeutical strategies.