ESR1 and breast cancer: Saussede-Aim et al. showed that 17β-estradiol exposure causes an up-regulation of βIII-tubulin in ERα-positive MCF7 breast cancer cells, and estrogen receptor modulators (e.g. tamoxifen) reduce the βIII-tubulin level in ERα-positive breast cancer cells, but did not affect the βIII-tubulin level in ERα-negative MDA-MB-231 cells[69].