ESR1 and breast carcinoma: We have previously identified low tumor levels of Nuc-pYStat5 as an indicator of poor prognosis and failure to respond to antiestrogen therapy in estrogen receptor-positive breast cancer patients.17 Thus, to further compare the two fluorescence immunohistochemistry methodologies and to determine if data derived from independent platforms yielded similar prognostic utility, we performed survival analysis on the estrogen receptor-positive subset of breast cancer patients from Cohort 1 for whom clinical outcome data was available.