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
Monoclonal antibody used in Head and neck cancer is:- 
Select and explain. 
A. Pembrolizumab, B. Trastuzumab, C. Rituximab, D. Ocralizumab
A: Pembrolizumab
Answer: A: Pembrolizumab 
Explanation: Drug Mechanism of action Uses Pembrolizumab Monoclonal antibody against PD 1 * Multiple myeloma * Non small cell lung cancer * Head and neck cancer * Any cancer containing mismatch repair Trastuzumab Monoclonal antibody against her-2/neu Breast cancer, gastroesophageal junction cancer Rituximab Monoclonal antibody against CD20 Non hodgkin's lymphoma(NHL), chronic lymphocytic leukemia(CLL) Ocrelizumab Monoclonal antibody against CD20 Primary progressive multiple sclerosis(PPMS)