This genetic test provides a window into a breast cancer patient's prognosis. From a biopsied sample of breast tissue, Oncotype Dx extracts 21 genes that are known to be involved in breast cancer. By analyzing how active these genes are, the test can predict how likely it is that a woman's cancer will recur, as well as which chemotherapy agents will be most effective against her tumor. Oncotype Dx is designed for newly diagnosed patients whose cancer has not spread to the lymph nodes and contains estrogen receptors. The test's makers are currently studying whether the screen can be as useful for women whose early-stage cancers have begun to spread.