Abdominoperineal resection is done in colorectal carcinoma on the basis of:

In the treatment of rectal cancer, distance of the tumor from the Dentate line is taken into consideration. LAR is done when tumor is situated 2cms from the dentate line so that 2cms of normal tissue can be resected below the dentate line. If 2cms of normal tissue cannot be resected below the tumor (but above the dentate line), APR procedure is done. Distance from the dentate line is not given among the option so distance from the anal verge is answer of choice here as dentate line is just 2cms from the anal verge. Ref: Devita's Oncology 8/e, Chapter 39, section 13; CSDT 13/e, Page 664; Schwaz 9/e, Page 1028; Sabiston 18/e, Page 1413.