This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Medicine
[{'content': 'Which one of the following drugs is the most common cause of progressive multifocal leukoencephalopathy? \nSelect and explain. \nA. Natalizumab, B. Cituximab, C. Rituximab, D. Bevacizumab', 'role': 'user'}, {'content': "Answer: A \nExplanation: Causes of progressive multifocal leukoencephalopathy:AIDSHematological malignanciesTransplant recipientsChronic inflammatory diseasesNatalizumab, a humanized monoclonal antibody(ref:Harrison's 18/e p3427)", 'role': 'assistant'}]