ESR1 and breast cancer: Previous studies have found that fluorescence immunohistochemistry by AQUA has greater sensitivity than pathologist-evaluated chromogen immunohistochemistry.2, 10, 11 To compare the newer ScanScopeFL/TissueStudio fluorescence immunohistochemistry technology to pathologist-evaluated chromogen immunohistochemistry, we further evaluated the estrogen receptor-positive breast cancers from Cohort 1 for levels of Nuc-pYStat5 using traditional pathologist scoring of chromogen immunohistochemistry.