Genes in this early response class represent potential therapeutic targets to delay or prevent brain metastasis using drugs already in use for other purposes, including Alpl, Arg2, Bcl2, C3, Chrm3, Kit, Maoa, and Odc1 (see http://www.voxvill.org), with the essential caveat that the contributions of these genes to the fitness of the metastatic tumor are unknown. The gene discussed is ARG2; the disease is metastatic neoplasm.