ERBB4 and breast cancer: The estimated pooled HRs implied that the elevated/positive expression of HER4 was a favorable indicator of RFS in HER2-positive breast cancer (HR = 0.53, CI: 0.40–0.71, P < 0.001, fixed effects; Figure 3C), and there was no statistical significance in the heterogeneity test (P = 0.11, I2 = 50.0%).