MMP-9, an enzyme that when secreted digests extracellular matrix to aid in invasion and metastasis typical of cancer cells (Morelli et al. 2004), including those produced by arsenic (Achanzar et al. 2002), showed marked increases between 16 and 18 weeks of arsenic exposure in WPE-stem cells (Figure 1A). The gene discussed is MMP9; the disease is cancer.