Table 2 Cox regression analyses of relapse-free survival and overall survival by HER2 and hormone receptor status

 Overall: HER2-low vs HER2-zero

0.88 (0.82–0.93)

< 0.001

–

0.90 (0.85–0.96)

0.002

–

 Hormone receptor-positive: HER2-low vs HER2-zero

0.92 (0.86–0.99)

0.022

0.973

0.90 (0.84–0.97)

0.004

0.715

 Hormone receptor-negative: HER2-low vs HER2-zero

0.92 (0.81–1.05)

0.226

0.92 (0.81–1.05)

0.244

 Overall: HER2 IHC1+ vs HER2-zero

0.85 (0.79–0.91)

< 0.001

–

0.89 (0.83–0.96)

0.001

–

 Overall: HER2 IHC2+ ISH− vs HER2-zero

0.96 (0.87–1.06)

0.421

0.94 (0.85–1.05)

0.280

 Hormone receptor-positive: HER2 IHC1+ vs HER2-zero

0.89 (0.82–0.96)

0.004

0.962

0.89 (0.82–0.96)

0.003

0.934

 Hormone receptor-positive: HER2 IHC2+ ISH− vs HER2-zero

1.01 (0.90–1.13)

0.898

0.94 (0.83–1.05)

0.280

 Hormone receptor-negative: HER2 IHC1+ vs HER2-zero

0.88 (0.76–1.03)

0.107

0.91 (0.78–1.05)

0.206

 Hormone receptor-negative: HER2 IHC2+ ISH− vs HER2-zero

1.04 (0.83–1.30)

0.735

0.97 (0.78–1.22)

0.807

 Overall: HER2-low vs HER2-zero

0.82 (0.76–0.89)

< 0.001

–

0.86 (0.79–0.93)

< 0.001

–

 Hormone receptor-positive: HER2-low vs HER2-zero

0.89 (0.81–0.97)

0.012

0.401

0.87 (0.79–0.96)

0.004

0.538

 Hormone receptor-negative: HER2-low vs HER2-zero

0.82 (0.69–0.96)

0.017

0.82 (0.70–0.97)

0.018

 Overall: HER2 IHC1+ vs HER2-zero

0.79 (0.73–0.87)

< 0.001

–

0.85 (0.78–0.93)

0.001

–

 Overall: HER2 IHC2+ ISH− vs HER2-zero

0.91 (0.79–1.04)

0.148

0.88 (0.76–1.01)

0.062

 Hormone receptor-positive: HER2 IHC1+ vs HER2-zero

0.86 (0.78–0.96)

0.005

0.627

0.86 (0.78–0.95)

0.004

0.811

 Hormone receptor-positive: HER2 IHC2+ ISH− vs HER2-zero

0.96 (0.82–1.12)

0.632

0.89 (0.76–1.05)

0.171

 Hormone receptor-negative: HER2 IHC1+ vs HER2-zero

0.78 (0.65–0.94)

0.009

0.82 (0.68–0.99)

0.035

 Hormone receptor-negative: HER2 IHC2+ ISH− vs HER2-zero

0.94 (0.71–1.24)

0.654

0.83 (0.62–1.09)

0.178