The impact of the 21-gene recurrence score assay on decision making about adjuvant chemotherapy in early-stage estrogen-receptor-positive breast cancer in an oncology practice with a unified treatment policy

Background: The 21-gene recurrence score (RS) assay has been validated in retrospective studies as prognostic of distant disease recurrence and predictive of the benefit of adjuvant chemotherapy in estrogen-receptor-positive breast cancer (BC). There is limited published data on the impact of the assay on clinical practice, particularly in the context of a single practice with a unified treatment policy. Patients and methods: Between 2006 and 2009, RS was obtained on 135 patients in a single practice with a uniform treatment policy. Treatment recommendations before and after RS result were analyzed retrospectively. Pre-RS treatment recommendations were based on clinicopathological features and Adjuvant! Online (AO) calculated survival advantage. RS and AO survival advantage for adding chemotherapy were compared for each patient. Results: The distribution by risk group of RS was low- 49.6%, intermediate-37.8%, and high-12.6%. In 34 patients (25.2%, 95% confidence interval 17.9% to 32.5%), recommendation for chemotherapy was changed after obtaining assay result. Most changes (70.6%) were from chemotherapy to no chemotherapy. The RS correlated poorly with AO predictions. Conclusion: The 21-gene assay, when applied in a consistent manner in early-stage BC, changes treatment recommendations in one-quarter of patients tested.