In breast cancer and melanoma - where protective effects were most pronounced (HR=0.27-0.50) - high β2-adrenergic receptor (β2-AR) expression enables effective blockade of catecholamine-driven metastasis pathways (cAMP/PKA/MMP-9) while simultaneously reversing immune suppression through PD-L1 downregulation and CD8+ T-cell enhancement. This evidence concerns the gene MMP9 and breast cancer.