Rectal cancer is often diagnosed by the following two methods in clinic: 1. Rectal fingerprinting: it is a simple and very important diagnostic method. Rectal fingerprinting can clarify the shape, texture, whether the base of the tumor is fixed or not, and whether it is easy to bleed, and so on, so that it can be initially judged whether it is rectal cancer or not; 2. Rectal microscopy: for the middle and lower rectal cancers, the tumors can be directly observed through the rectal microscopy in the clinic; for the higher position rectal cancers, complete colonoscopy should be carried out. For rectal cancer with higher location, complete colonoscopy should be carried out. A biopsy, i.e. pathologic examination, is taken under the colonoscope. It can confirm the diagnosis of rectal cancer, and very few patients can have colorectal cancer in multiple sites, which is called multiple colorectal cancers. Through complete colonoscopy, it can reduce the chances of missed diagnosis, so rectal pathology biopsy is the most important way to confirm the diagnosis of rectal cancer.