Colon cancer symptoms depend on the location of the tumor—right colon or left colon.
Cancers of the larger and more pliable right colon frequently bleed, causing anemia , but do not usually block the colon because the stool is still liquid in the right side of the colon.
Cancers in the left colon may obstruct the bowel, causing a change in bowel habits and stool size. There may be dark red rectal bleeding or blood in the stools, which may be long and narrow.
Cancers in the rectum may cause an obstruction, causing a change in bowel habits (including constipation) and in the size of stools, which may become long and narrow. There may also be rectal bleeding. Other symptoms include abdominal or pelvic pain, gas, vomiting, persistent constipation or diarrhea, weight loss and weakness. Pain is a worrisome problem with rectal cancer, since it often means the tumor is growing into nerves.
