Consistent with our assumption, pterostilbene has a dose-dependent inhibition on the phosphorylation of p38 kinase, a hallmark of kinase activation, but not the phosphorylation of ERK1/2 in HRG-β1-stimulated cells (Figures 7(a) and 7(b)), indicating that down-regulation of p38 kinase pathway might be one of the possible reasons for suppression of HRG-β1-elicted MMP-9 induction and invasion of breast cancer cells by pterostilbene. The gene discussed is MMP9; the disease is breast cancer.