How do you treat GIST with de-differentiation to pleomorphic sarcoma on chronic therapy with imatinib?  

Once a GIST, always a GIST.  Sarcomas that are driven by a translocation can behave badly but they never ever get rid of their translocation. Possibly by saying the GIST has de-differentiated your pathologist is telling you the GIST looks more aggressive.  Or maybe it was never was GIST i...