This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Rectum and anal canal, Subject name: Surgery
[{'content': 'Commonest type of carcinoma anal canal is: \nSelect and explain. \nA. Adenocarcinoma, B. Squamous cell carcinoma, C. Adenocanthoma, D. Papillary type', 'role': 'user'}, {'content': 'Answer: B \nExplanation: CARCINOMA ANAL CANAL MC type of CA anal canal : SCC > BCC > Melanoma Median age at diagnosis :60 years MC symptom : Bleeding PR MC site of metastasis: Lung MC site of LN metastasis : Inguinal LNs', 'role': 'assistant'}]