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': 'Least common cause of clubbing is: \nSelect and explain. \nA. Adenocarcinoma, B. Squamous cell cancer, C. Small cell cancer, D. Mesothelioma', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Lung cancer is the most common cause of clubbing . Most common with adenocarcinoma and is least common with small cell lung cancer.', 'role': 'assistant'}]