In this study on mice, sensitivity of resistant ER+ cancer to Tamoxifen is restored when using a chemical called disulfide benzamide, or DIBA.
If this feat can be safely duplicated in women it may not only prevent progression of ER+ tumours but also possibly reduce the risk of inducing HER+ cancer since it has been shown in previous studies that in some cases adminstration of Tamoxifen for at least 3 months after start of resistance causes genetic changes leading to the more agressive HER+ tumours.
http://www.cancer.gov/newscenter/pre...ifenResistance
Researchers Discover Method in Mice to Restore Tamoxifen Sensitivity in Resistant Breast Cancer