Women's Health: Gene test predicts response to breast cancer drug

A test that characterizes each breast tumour by its unique genetic fingerprint may soon allow doctors to identify those women whose cancer is most likely to recur despite treatment with a common medication for the disease.

The powerful genetic tool can help spare many women from unnecessary treatment that is doomed to fail, says researcher Dr. Marleen Kok of the Netherlands Cancer Institute in Amsterdam.

The test looks for the presence of 81 genes involved in response to tamoxifen, a drug that interferes with the growth-promoting effects of the female hormone estrogen on the tumour. Currently, doctors rely on tests that detect levels of hormone receptors to decide if a woman should get tamoxifen.

"But those tests don't tell us the whole story," says Dr. C. Kent Osborne, head of the cancer centre at the Baylor College of Medicine in Houston. "Having a test like this would be a real advantage."

For the study, researchers tested the genetic 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 per cent of non-responders – women (whose cancer) progressed despite tamoxifen therapy," Kok says.

The researchers then compared the new test with other predictors of tamoxifen response, including menopausal status, aggressiveness of the cancer, and levels of receptors for estrogen and progesterone hormones.

They found the gene test outperformed all the predictors except progesterone receptor levels. 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.

Further studies may indicate whether the genetic test will help doctors identify women whose cancer is likely to spread despite treatment with other drugs called aromatase inhibitors. "If we know a woman is resistant to tamoxifen, we can start her on an aromatase inhibitor," Kok says. "If we know she's also resistant to aromatase inhibitors, we can offer chemotherapy."