In contrast, our xenograft model is a reproducible model of human GIST that replicates the intraperitoneal microenvironment and heterogeneity of human GISTs while allowing for the development of models (i.e., KIT exon 9 mutated GIST) that are not currently available for study in GIST cells or transgenic mouse models. The gene discussed is KIT; the disease is gastrointestinal stromal tumor.