The key genes identified for luminal A breast cancer were GRM4, GRM8, KRT18, NMUR1, MUC1, CX3CL1, GATA3, and NCAM1. The neuroactive ligand–receptor interaction pathway was enriched for GRM4, NMUR1, and GRM8 (P < 0.05). This evidence concerns the gene GRM8 and breast cancer.