This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Targeted Anticancer Drugs and Immunosuppressants, Subject name: Pharmacology
Which of the following agents is recommended as first line drug for treatment of gastrointestinal stromal tumors (GIST)? 
Select and explain. 
A. Sorafenib, B. Geftinib, C. Imatinib, D. Erlotinib
C: Imatinib
Answer: C: Imatinib 
Explanation: Imatinib is drug of choice for GIST. Imatinib resistant cases can be treated with sunitinib. Tumors resistant to both imatinib and sunitinib are treated with regorafenib.