NPY1R and breast cancer: Remarkably, knockdown of NPY1R significantly inhibited the growth of T47D WT cells under E2 stimulation, as well as the ligand-independent growth of ESR1 mutant cells (Fig. 5H and Supplementary Fig. 7C), underscoring the essential role of NPY1R in estrogen-dependent and ESR1 mutant breast cancer cell growth.