Dec. 19, 2006 (San Antonio) -- A test that characterizes each breast tumor by its unique genetic fingerprint may soon allow doctors to identify those women whose cancer is most likely to recur despite tamoxifen therapy, Dutch researchers report.
The powerful genetic tool can help spare many women from unnecessary treatment that is doomed to fail, says researcher Marleen Kok, MD, of the Netherlands Cancer Institute in Amsterdam.
The test, which looks for the presence of 81 genes involved in tamoxifen response, was described at the San Antonio Breast Cancer Symposium (SABCS).
Currently, doctors rely on tests that detect levels of hormone receptors to decide if a woman should get the hormone drug tamoxifen. That's because the drug tends to benefit women whose cancers are fueled by hormones.
"But those tests don't tell us the whole story," says SABCS Co-director C. Kent Osborne, MD, head of the cancer center at Baylor College of Medicine in Houston.
Optimizing Breast Cancer Treatment
For the study, which employed a commercially available gene chip, the researchers tested and then validated the technique on frozen tissue samples from more than 60 women with breast cancer who were treated with tamoxifen.
The tissue samples, about one-third the thickness of a sheet of paper, were sent to a lab for analysis.
"We found that the test correctly classified 84% of nonresponders -- women who progressed despite tamoxifen therapy," Kok says.
The researchers then compared the new test to other predictors of tamoxifen response, including whether a woman had reached menopause, the aggressiveness of her cancer, and levels of estrogen receptors and progesterone receptors.
They found that the gene test outperformed all the predictors except the progesterone receptor test. And when the gene test and progesterone receptor test were used in combination, they got the best results of all.
"Using the two tests together will optimize treatment selection," Kok says.
Though it has yet to be tested, the genetic screen will presumably also help doctors identify women whose cancer is likely to spread despite treatment with newer hormone drugs called aromatase inhibitors, she says.
That's the next step, according to Kok. "If we know a woman is resistant to tamoxifen, we can start her on an aromatase inhibitor. If we know she's also resistant to aromatase inhibitors, we can offer chemotherapy," she says.