GPER1 and breast cancer: Chen et al. [25] proposed a plasmonic fiber Bragg grating biosensor for the detection of breast cancer cells, which, after coating with a gold nanofilm and immobilizing an antibody against GPR30, demonstrated the ability to detect breast cancer cells at concentrations as low as 5 cells/mL within 20 minutes, with a linear range of 5–1,000 cells/mL suitable for real-world CTC detection.