ESR1 and breast cancer: To investigate the clinicopathological significance of the association between BIG3 expression and PHB2-S39 phosphorylation levels in breast cancer, we performed immunohistochemistry analyses of 82 primary ERα-positive breast cancer specimens and classified these into four levels of BIG3 expression (score: 0 to +3; see Methods) (Fig. 4a; Supplementary Table 2).