This anti-apoptotic effect of OPN, through β-catenin-mediated up-regulation of anti-apoptotic protein Mcl-1, also antagonized imatinib-induced apoptosis in GIST in vitro, suggesting a potential role of OPN and Mcl-1 in the mechanism underlying drug resistance to imatinib in GIST patients. This evidence concerns the gene SPP1 and gastrointestinal stromal tumor.