ESR1 and metastatic neoplasm: Multivariable analysis adjusting the impact of HER2 status on PFS for clinically relevant covariates (age, ERα expression, Ki-67 expression, number of metastatic sites, disease-free interval [DFI], de novo metastatic disease, ECOG performance status [PS], liver metastases and type of ET) confirmed an independent and statistically significant association between HER2-low status and worse PFS (adjusted hazard ratio [aHR] 1.42; 95% confidence interval [CI]:1.07–1.89; p = 0.0163) (Table 1).