This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
Preferred initial treatment for Ca anal canal is 
Select and explain. 
A. Surgery, B. Chemoradiation, C. Immunotherapy, D. Observation
B: Chemoradiation
Answer: B: Chemoradiation 
Explanation: Anal cancer Uncommon tumour, which is usually a squamous cell carcinoma Associated with HPV More prevalent in patients with HIV infection May affect the anal verge or anal canal Lymphatic spread is to the inguinal lymph nodes Treatment is by chemoradiotherapy in the first instance Major ablative surgery is required if the above fails Ref: Bailey & Love&;s Sho Practice of Surgery,E25,Page-1269