This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lung Tumor, Subject name: Pathology
[{'content': 'A 67 yr male with history of chronic smoking hemoptysis with cough. Bronchoscopic biopsy from centrally located mass shows undifferentiated tumor histopathologically. Most useful I.H.C. (immunohistochemical) marker to make a proper diagnosis would be: \nSelect and explain. \nA. Cytokeratin, B. Parvalbumin, C. HMB-45, D. Hep-par1', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The presence of chronic smoking, cough and hemoptysis in old man is a pointer towards a diagnosis of bronchogenic cancer. The central location suggests the possibility of a squamous cell cancer. Histologically, this tumor is characterized by the presence of keratinization and/or intercellular bridges. HMB (melanoma), Hep par1 (liver cancer) and parvalbumin (schizophrenia).', 'role': 'assistant'}]