Since the lack of nutlin-3 response is predictive of dysfunctional p53 we performed quantitative RT-PCR for p53 and MDM2 following nutlin-3, RITA and doxorubicin treatment, which did not result in a detectable induction of p53 in GIST882 and GIST-T1. This evidence concerns the gene MDM2 and gastrointestinal stromal tumor.