The influence of the 21-gene recurrence score assay on decision making about adjuvant chemotherapy in stage I-II estrogen receptor-positive breast cancer: Experience at a single center with a uniform treatment policy.

660 Background: The 21-gene assay (OncotypeDx) recurrence score (RS) has been validated in retrospective studies as prognostic of distant disease recurrence and predictive of benefit of chemotherapy in estrogen receptor (ER)-positive breast cancer. Published data on the impact of the assay on clinical practice is limited. We analyze the influence of the RS on decision making in 135 patients seen in a single practice with a unified treatment policy. Methods: Patients with stage I and II breast cancer, ER-positive, Her2-negative who had no contraindications to chemotherapy were eligible. Clinical and pathologic data were recorded, as was the recommendation on adjuvant chemotherapy both before and after obtaining the RS. The test was performed by Genomic Health (Redwood City, CA, USA) on paraffin imbedded tissue from surgical specimens or biopsies. Our treatment policy was to give adjuvant chemotherapy for high risk RS (> 30), endocrine therapy alone for low risk RS (< 18), and for intermediate risk RS (18-3...