In order to investigate novel mechanisms of hormonal therapy resistance (HTR) in breast cancer, we examined the expression of ERα protein in different BC cell lines, either in the absence or presence of the selective estrogen receptor degrader (SERD) fulvestrant (ICI 182,780) which reduces ERα full-length (ERα-FL, 66 kDa) protein levels as a consequence of reduced stability and dimerization22,23. Here, ESR1 is linked to breast cancer.