A 56 year old man has been having bloody bowel movements on and off for the past several weeks. He repos that the blood is bright red, it coats the outside of the stools, and he can see it in the toilet bowl even before he wipes himself. When he does so, there is also blood on the toilet paper. After fuher questioning, it is asceained that he has been constipated for the past 2 months and that the caliber of the stools has changed. They are now pencil thin, rather the usual diameter of an inch or so that was customary for him. He has no pain. Which of the following is the most likely diagnosis?

The combination of red blood coating the stools and a change in bowel habit and stool caliber spells out cancer of the rectum in someone in this age group. Anal fissure is typically seen in young women who have very painful bowel movements with streaks of blood. Pain is the dominant symptom in this condition. Cancer of the cecum leads to anemia and occult blood in the stools, but the blood is rarely seen. If it is, the entire stool is bloody. Fuhermore, there is no change in bowel habit or stool caliber when the tumor is so proximal in the colon. External hemorrhoids hu and itch, but they rarely bleed. Ref: Chang G.J., Shelton A.A., Welton M.L. (2010). Chapter 30. Large Intestine. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.