An encircling adenocarcinoma of the rectosigmoid region is seen here. There is a heaped up margin of tumor at each side with a central area of ulceration. This produces the bleeding that allows detection through a stool guaiac test. Normal mucosa appears at the right. The tumor encircles the colon and infiltrates into the wall. Staging is based upon the degree of invasion into and through the wall. The colonoscopic views of a smaller rectal adenocarcinoma, but still with an ulcerated surface, are shown below.