ESR1 and breast cancer: As shown in Figure 6B, the co-treatment with AZD4547 induced enhanced inhibition of both pERα/S118 and pERα/S167 in both cell lines, particularly MCF-7/FGFR1 cells, indicating that FGFR1 activation leads to enhanced ERα phosphorylation, and co-targeting PI3K and FGFR1 is effective in blocking ER signaling in alpelisib-treated breast cancer cells.