Narrator:       This is Science Today. For thousands of breast cancer patients, the drug tamoxifen has been something of a miracle worker, shrinking tumors and inhibiting cancer growth. But over time, many of these patients acquire resistance to the drug, reducing its effectiveness. Oncologist Pamela Munster and a team of researchers at the University of California, San Francisco, has discovered how this resistance occurs and a potential way to overcome it.

Munster:        For many years we thought that tumors have certain mutations that makes them resistant to drugs. But what we learned is tumors can also develop a way to escape drugs and develop resistance and the way that these tumors do this is by taking a gene and modifying it with what we call epigenetic modification.

Narrator:       This means that the tumors can change gene expression within a single generation, adapting quickly to the presence of a drug such as tamoxifen. Understanding this mechanism may lead to supplementing tamoxifen with drugs that can reprogram epigenetic modification. For Science Today, I'm Larissa Branin.