ESR1 and breast cancer: In breast cancers, Sox2 is a weak prognostic factor, but has been associated with poor disease-free survival by univariate analyses (10, 13, 14, 33) and multivariate analyses, independently of the nodal stage, ER and HER2 (14) or independently of tumor size, nodal stage and PR (10), and poor overall survival, by univariate analyses only (13, 33).