ERBB2 and breast cancer: We also evaluated whether Ki67 IHC cut-off points (≤ 5%, ≥ 30%) could accurately identify patients with either low 21-gene RS (< 26) or high RS (≥ 26) among a clinically low-risk group of early-stage breast cancer patients, who we defined as women aged 50 + years diagnosed with ER+PR+HER2−, node-negative disease.