Molecular pathways: digoxin use and estrogen-sensitive cancers--risks and possible therapeutic implications.

Digoxin, a phyto-estrogen, binds with estrogen receptors (ER) and can cause gynecomastia. Among women currently using digoxin, breast and uterus cancer incidences are significantly increased (approximate risk ratios, 1.3-1.5). Both cancers are often estrogen sensitive. In contrast, ovary and cervix cancers are relatively estrogen insensitive, and incidence is unaffected by digoxin exposure. When digoxin use stops, incidence rapidly reverts to that in nonusers. These patterns parallel those of estrogen, suggesting that digoxin works via ER-stimulated proliferation of ductal and/or acinar cells, accelerating the growth of nascent cancers. Also consistent with an estrogenic effect, men using digoxin have a small but significant reduction in prostate cancer (risk ratio, 0.76). Other estrogen-like drugs, particularly spironolactone, should be investigated for similar effects. The effect of digoxin use in women being treated for breast cancer or in survivors is unknown. Women with estrogen-sensitive cancers on adjuvant therapy may take tamoxifen, which blocks ERs. However, postmenopausal patients may use aromatase inhibitors, which block estrogen production while leaving ERs susceptible to digoxin. If adverse effects are found, tamoxifen may be preferred over aromatase inhibitors in patients receiving estrogen-mimicking drugs. Alternatively, other cardiotropic drugs might be considered in women with or at high risk of developing estrogen-sensitive cancers.