Colon cancer is one of the most common types of cancer in the Western world and the second-leading cause of cancer deaths. More common among women, incidence of colon cancer begins to rise at age 40 and peaks between ages 60 and 75. Early detection by colonoscopy is crucial because in its early stages, colon cancer rarely causes symptoms. As it progresses, a number of side effects may arise.
Fatigue and Weakness
Tumors cause bleeding and may be seen as dark red streaks in the stool, bright red rectal bleeding or traces of blood, called occult blood. This bleeding can cause iron deficiency anemia. Because red blood cells carry oxygen, anemia can lead to fatigue and weakness. An article in the International Journal of Colorectal Disease in 2000 found that iron deficiency anemia with a positive occult blood test are closely related to the presence of colon cancer.
Changes in Bowels
As described in the Merck Manual, tumors in the colon can grow into the colon opening or can encircle it. Stool passes from the larger right side, the ascending colon--where the stool is mostly liquid and easily passes through a narrowed opening--to the smaller descending colon on the left side, where the stool is semi-solid. A tumor on the left side may cause thin stools, a feeling of incomplete elimination, diarrhea or constipation.
Unexplained Weight Loss
All types of cancer may be associated with unexplained weight loss. The American Cancer Society says cancer cells use a lot of energy, stealing it from the body. The cells may also release substances that change the way the body makes energy from food. The Mayo Clinic notes that weight loss from cancer usually results in unexplained weight loss of at least 10 lbs. or 5 percent of total body weight.
Mass in the Abdomen
Colon cancer grows slowly, but undetected tumors can become quite large. The doctor may be able to feel a mass in the abdomen if a sizable tumor is present. The Merck Manual says that a tumor growing in the wider right side of the colon is more likely to get palpably large before it's detected. The stool passing through that area is liquid, so the tumor doesn't cause altered stools. Pressure from the tumor can cause significant discomfort.
