Test flags patients who will benefit from chemo: 'major breakthrough' in breast ca treatment.(News)

SAN ANTONIO -- A commercially available genetic test reliably predicts the magnitude of chemotherapy benefit in women with estrogen receptor-positive, lymph node-negative breast cancer--potentially enabling tens of thousands of women per year to safely avoid the toxicities and expense of adjuvant chemotherapy.

"This is a major breakthrough for the individualized treatment of patients diagnosed with early breast cancer," Soon-Myoung Paik, M.D., declared at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.

The 21-gene test, known as the Oncotype DX, was the subject of two large clinical studies and a favorable cost-benefit analysis presented at the San Antonio breast cancer symposium.

The test, developed and marketed by Genomic Health Inc., previously was shown to predict the likelihood of distant recurrence of tamoxifen-treated node-negative breast cancer.

In a new study, Dr. Paik applied the Oncotype DX to standard, routinely available tumor samples stored in paraffin blocks from 651 participants in the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-20 trial, in which women with node-negative, estrogen receptor-positive breast cancer were randomized 1:2 to tamoxifen alone or tamoxifen plus chemotherapy.

The rationale for applying the tumor gene-expression assay to this patient population lies in the fact that current guidelines recommend adjuvant chemotherapy in the great majority of such patients, yet prior studies demonstrate the clinical benefit is concentrated in only about 15% of the treated population. That means roughly 85% of early-stage breast cancer patients are being overtreated with chemotherapy, explained Dr. Paik, director of the division of pathology at the NSABP in Pittsburgh.

A total of 25% of participants in the B-20 trial proved to have a high recurrence score on the Oncotype DX, meaning at least 31 out of a possible 100 points. Their 10-year distant recurrence-free survival rate was 88% with chemotherapy and 60% without it.