ESR1 and breast cancer: By comparing the growth effects of FGF ligands on two subsets of ER + breast cancer cell lines: one with FGFR1 amplification (CAMA1, MDA-MB-134) and the other without (MCF7, T47D), our study not only validated the paradoxical growth effects across various FGF ligand types, but also delved into the mechanisms underlying these paradoxical growth effects.