ESR1 and cancer: However, the pCR rates in the combined IO arms for grade III, MP2, and ER-low are 45%, 56%, and 63%, respectively, versus 75% for ImPrint+, with similarly low pCR rates in grade I/II (11%), MP1 (15%), and ImPrint– (17%) cancers, and a 24% pCR rate in ER-low (Fig 4 and Appendix Fig A2v Figs 2 and 3).