Metastasis, the spread of tumor cells from a primary site and formation of a new colonization in distant organ site,remains one of the major challenges for effective cancer treatment.This is partially due to the lack of understanding of the molecular pathogenesis of metastasis.Recent advances in microarray analyses of metastatic tumors have unearthed several genes and genetic pathways that are associated with metastasis, but their critical roles in the pathogenesis of metastasis are still not well understood.To further validate these candidate metastatic genes and identify additional genes that play causative roles in metastasis, we have applied a genome-wide random mutagenesis strategy to screen for genes whose inactivation or activation/over-expression results in the gain of metastatic phenotype.