We focused on the gene expression signature of acidic pHe-treated B16-BL6 cells at two different pHe levels, such as pHe 6.8 as mild acidosis and pHe 5.9 (optimal pH for matrix metalloproteinase 9 (type IV collagenase, gelatinase B, MMP9) induction (15) contributing to tumor metastasis) as severe acidosis. This evidence concerns the gene MMP9 and neoplasm.