The Oncotype DX test measures the expression, or activity, level of 21 specific genes within a tumor sample and based on that pattern assigns a recurrence score of anywhere from 0 to 100. Earlier trials have shown that the higher the recurrence score, the more likely the patient's cancer will recur. The assay is performed by Genomic Health, Inc., based in Redwood City, California.

Oncotype DX is only one of several gene expression profile tests oncologists now use to help them judge how likely it is a patient's cancer will return or to inform treatment decisions. RxPONDER researchers plan to evaluate other tests as well, including the PAM50 test, which measures the expression level of a set of 50 genes to determine a patient's "risk of recurrence" score.

"There are larger questions here," says Laurence H. Baker, D.O., SWOG group chair and professor of internal medicine and pharmacology at the University of Michigan. "Can lab tests allow us to target follow-up chemotherapy in a much narrower and more effective way? And if so, which tests are most clinically effective for our patients and most cost effective?"

The TAILORx trial in node-negative breast cancer (cancer that has not spread to the patient's lymph nodes), which recently enrolled its final patient, used the Oncotype DX assay to select patients with mid-range recurrence scores for study, and will help identify in which of these patients adjuvant endocrine therapy alone is sufficient treatment. Final results of the TAILORx trial will not be known for several years.

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