Colon cancer may be found in the left side of the colon (producing a "napkin ring" or "apple core" appearance) or the right side of the colon (producing a polypoid mass). In either location, bleeding may produce an iron-deficiency anemia. Histologically, the vast majority of colon cancers are adenocarcinomas. Currently the most common classification used to stage colon carcinomas is the Astler-Coller modification of the Dukes classification of colon cancer. This classification is as follows: A = mucosa (or submucosa, arbitrary); B1 = into muscularis propria; B2 = through muscularis propria; C1 = into muscularis propria with lymph node metastasis; C2 = through muscularis propria with lymph node metastasis; D = distant spread. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition