ESR1 and breast cancer: The 479 cases of various types of breast cancers they analysed with IHC showed a high proportion of staining in ER/PR positive (95% of 176), HER2 positive (79% of 67) and TNBCs (81% of both 52 metaplastic and 184 non-metaplastic cases), being more sensitive than GATA3 for this latter subset.