ESR1 and breast cancer: In four different ER+ breast cancer cell lines tested (two of them luminal A and two of them luminal B), treatment with PI3K inhibitor BEZ-235 for 3 hours significantly increased expression of ER and ER-inducible target genes (PR, CAV1, and IGF1R); this result was observed by using two concentrations of the inhibitor (100 nM and 500 nM), with the higher concentration appearing to have a slightly more dramatic effect on the genes (Figure 4a).