In addition, metastatic disease involved ≥2 sites was an independent unfavourable prognostic factor for both HR−HER2+trast+ subgroup (HzR = 1.49, 95% CI: 1.07–2.07, P = 0.018) and HR+HER2+trast+ subgroup (HzR = 1.50, 95% CI = 1.05–2.14, P = 0.025) (Table 3). The gene discussed is ERBB2; the disease is metastatic neoplasm.