Secondary C-kit mutation is a cause of acquired resistance to imatinib in gastrointestinal stromal tumor.

C-kit gene gain of function mutations are important in the pathogenesis of gastrointestinal stromal tumors (GISTs). Imatinib is a selective tyrosine kinase inhibitor of KIT and achieves a partial response or stable disease in most patients with metastatic GIST, but there is increasing evidence of acquired resistance. We report a case of GIST with acquired resistance to imatinib during therapy and secondary c-kit mutation besides the primary mutation.