Scientists have found evidence that tamoxifen, the drug widely used to treat breast cancer, may lose its effectiveness over time and begin to behave like the hormone it is supposed to block. Tamoxifen works by blocking the action of estrogen and keeping it from attaching to a receptor on the surface of the cell.
Researchers at Duke University Medical Center have found that after a period of two to five years, the “anti-estrogen effect of tamoxifen fades, often allowing estrogen-sensitive cancers to start growing again.” The primary author of the study, John D. Norris, explained that “over time, the drug causes the estrogen receptor on cells to change and form a pocket-like structure that allows other proteins to bind there. The action of these proteins somehow changed the cell’s reaction to tamoxifen. The drug converts from an anti-estrogen effect to a pro-estrogen effect.”
However, the scientists have discovered that the action can be reversed with the use of peptides. They also believe that this will allow them the opportunity to find a new drug anti-estrogen drug that does not have the same effects as tamoxifen.