This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Commonest type of anal canal carcinoma is? 
Select and explain. 
A. Squamous cell carcinoma, B. Adenocarcinoma, C. Adenoacanthoma, D. Papillary type
A: Squamous cell carcinoma
Answer: A: Squamous cell carcinoma 
Explanation: Mainly three types of malignant neoplasm are seen in anal canal Squamous cell carcinoma (most common) Basal cell carcinoma (2nd most common) Melanoma Also remember: Most common type of rectal and colon cancer Adenocarcinoma Ref: S. Das textbook of surgery 3/e, Page 1078.