This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Neoplastic Agents, Subject name: Pharmacology
Drug of choice for treatment of gastrointestinal stromal tumors is: 
Select and explain. 
A. Rituximab, B. Imatinib mesylate, C. Anagrelide, D. Denileukin diftitox
B: Imatinib mesylate
Answer: B: Imatinib mesylate 
Explanation: Ans: B (Imatinib mesylate) Ref: Goodman & Gillman, The pharmacological basis of therapeutics, 12th edition, Pg No. 1732-1734.Explanation:Imatinib mesylate is used in the treatment of (Approved indications)Chronic phase of CIVILGIST- Gastrointestinal Stromal tumorChronic Myelomonocytic leukemiaHypereosinophilic syndromeDermatofibrosarconia protruberanceProgressive plexiform neurofibromatosisIt is also tried in (Experimental and Not approved for routine use)Systemic MastocytosisPulmonary hypertensionAlzheimer' s diseaseLowering or reversing opioid toleranceDesmoid tumor