Breast carcinoma with 21-gene recurrence score lower than 18: rate of locoregional recurrence in a large series with clinical follow-up.

Our study of node negative, ER+/HER2- breast cancer patients with low RS observed extremely low rates of LRR: 0.9% (13/1396) in the whole cohort and 0.7% (8/1184) in patients treated with endocrine therapy alone. As the largest series to date, we report detailed clinicopathologic data and clinical outcomes of this cohort and provide a comprehensive characterization of patients who developed LRR.