29 Background: In 2010 the National Comprehensive Cancer Network recommended a 21-gene assay recurrence score (RS) to aid in the adjuvant treatment decision among patients with estrogen receptor positive, lymph node negative early stage breast cancer. Early-decision impact studies show that the RS can reduce overall chemotherapy use by 27%. This study was performed to assess the cost-benefit of the test for the patients diagnosed and treated an academic institute before 2010. Methods: Data from early breast cancer estrogen-receptor–positive and lymph-node–negative patients (n = 87), who were diagnosed and treated at our center from 2004-2010 were analyzed. All patients had the 21-gene recurrence test done to guide in their management. Cost of chemotherapy, adverse effects, and supportive care costs were calculated from previously published articles. Results: 66 patients with stage I breast cancer and 21 patients with stage II were analyzed. All but one patient had a tumor size more than 5mm. In total, 27 patients received chemotherapy. Characteristics of patients receiving chemotherapy are shown in the table. Cost of 21 gene recurrence score assay was $4,000. Savings for each patient who did not receive chemotherapy was $21,715 after accounting for cost of the test. The total savings for 60 patients who did not receive chemotherapy was $1,302,900. Conclusions: Use of the 21-gene assay in patients with early stage lymph node negative breast cancer improves health outcomes by avoiding chemotherapy-related adverse events. It also appears to add no incremental costs. This study emphasizes the cost-saving potential of the Oncotype Dx 21 gene assay. [Table: see text]