Application of RSClin to guide treatment recommendations for premenopausal patients with early-stage hormone-positive breast cancer and intermediate risk oncotype recurrence scores.

e12511 Background: The RSClin model, which incorporates the Oncotype Recurrence Score (RS) and clinicopathologic features, was recently developed to further tailor prognosis and prediction of chemotherapy benefit for patients with early-stage hormone positive (HR+) breast cancer (BC) (Sparano et al, 2020). The RSClin calculator is available online to assist treatment planning for situations where chemotherapy benefit is uncertain. Covariates include Oncotype RS, tumor grade, tumor size and patient age. The risk calculator generates a 10-year distant recurrence risk and absolute chemotherapy benefit. This tool may be especially helpful to determine treatment management for premenopausal patients with early-stage HR+ BC with intermediate risk (IR) Oncotype RS (16-25). We retrospectively applied RSClin to this patient population to determine if it would have changed treatment recommendations. Methods: We identified premenopausal women with node-negative early-stage BC with IR RS (16-25) within our large Oncotype database. Using the RSClin model, we selected >5% absolute chemotherapy benefit as a reasonable cutoff to recommend chemotherapy. We compared the treatment recommendation based on RSClin with the treatment previously recommended by breast oncologists at our large academic medical center in New York City. Results: There were 86 patients who met criteria with a median age of 46 years. Of these, 26 patients (30%) were recommended chemotherapy plus endocrine therapy (ET) and 60 (70%) were recommended ET alone. After applying the RSClin model (data available for 83/86 patients), 19 (23%) would have resulted in a change in treatment recommendation and 64 (77%) would have remained unchanged. Overall, 8 (10%) would have withheld chemotherapy when it was previously offered and 11 (13%) would have recommended chemotherapy when it was previously excluded. There were 8 (9%) secondary invasive breast events in this population, with 2 (2%) being ipsilateral, 3 (3%) being contralateral and 3 (3%) metastatic at a median follow up of 46.9 months. Conclusions: The RSClin model would have changed management of premenopausal patients with IR RS in 23% of patients. This model, although not yet prospectively validated, may help individualize therapy for patients with less definitive treatment plans. Using RSClin, we can aim to minimize recurrence rates and avoid unnecessary chemotherapy in selected patients. This model is easy to apply and will have important clinical utility moving forward.