Tamoxifen has been used successfully for over 20 years. The researchers know that over time Tamoxifen can lose its effectiveness. Many women diagnosed with Stage IV breast cancer that have tumors that are estrogen-receptor positive can be put on Tamoxifen to control the disease. After some time the patient becomes resistant to Tamoxifen and has to be switched to another drug.

A molecule, called disulfide benzamide or DIBA, could provide a way to overcome that resistance and restore the effectiveness of Tamoxifen. Findings are published in the December issue of Cancer Cell that show how mice engineered to develop Tamoxifen resistant tumors and human breast cancer cells in the lab were given the molecule. In both cases the tumor growth slowed.

William Farrar, head of the Cancer Stem Cell Section of the National Cancer Institute's Center for Cancer Research and the studies lead author, says "DIBA is what is known as a lead compound, which means it merely opens the door to suitable drugs." He also says that "DIBA itself is probably not appropriate for humans, because of solubility problems". The team plans to try and develop another compound fashioned after the properties of DIBA and hopeful have this be able to be administered orally.

One important aspect of the research was that it focused only on an acquired resistance to Tamoxifen over time. It did not study why some estrogen positive tumors initially are resistant to the drug.