By contrast, there were no significant differences in IDFS and DRFS between patients with HER2-low and HER2-zero in the low recurrence-risk group (i.e., in cohort 2: patients with 1–3 positive ALNs, HG < 3, tumor size < 5 cm, and high Ki-67 index (≥ 20%), and in cohort 3: patients with 1–3 positive ALNs, HG < 3, tumor size < 5 cm, and low Ki-67 index (< 20%)). The gene discussed is ERBB2; the disease is neoplasm.