ESR1 and breast cancer: We have therefore (a) characterized gene expression, protein, and/or amplification levels for ER and HER2 individually; (b) explored the relation between ER and HER2 at both the protein and RNA levels, irrespective of the samples ER and HER2 status; and (c) evaluated the significance of transcript levels within the HER2-ve population and, in particular, the ER+veHER2-ve/subgroup in terms of relapse-free survival in a set of 448 early breast cancers from the NCRI Adjuvant Breast Cancer (ABC) Trial-Tamoxifen Late Relapse Study [25,26].