SPP1 and gastrointestinal stromal tumor: Our study suggests that OPN, with its igniting or initiating role of specific anti-apoptotic signaling transduction via up-regulation of anti-apoptotic protein Mcl-1 and its significant anti-apoptotic effect on inhibiting imatinib-induced apoptosis, may be a potential and promising target for pharmaceutical intervention in GIST resistant to conventional imatinib treatment.