SPP1 and gastrointestinal stromal tumor: This anti-apoptotic effect of OPN, through β-catenin-mediated up-regulation of anti-apoptotic protein Mcl-1, was able to attenuate imatinib-induced apoptosis in GIST in vitro, suggesting a possible role of OPN and Mcl-1 in the mechanism underlying drug resistance to imatinib in GIST patients.