Tamoxifen is a drug with a dual personality.
It can dramatically reduce the recurrence of breast cancer in women with estrogen-receptor positive tumours, and may even prevent the initial occurrence of the disease in women at high risk. And the change appears inevitable. We've known for a long time that tamoxifen has this dual activity in certain genes. Because of this treacherous trait, resistance to tamoxifen may well be inevitable in women with metastatic breast cancer. There is also evidence that women who take more than five years of tamoxifen therapy have worse outcomes than women who stop at that time, Dr. Osborne said.