Douglas A. Nelson, MD, is a board-certified oncologist and hematologist who previously served for 13 years as a physician in the US Air Force.
The term colon cancer is sometimes used interchangeably with colorectal cancer because colon and rectal cancers share common features. The rectum and colon make up the large intestine. Colorectal cancer is the fourth most common cancer in the United States, and it’s the second leading cause of cancer-related deaths.
Most colon cancers are caused by growths within the inner lining of the colon, called polyps. The chance of a polyp developing into cancer depends on factors, like the type of polyp (adenomatous polyps are considered precancerous) or if it has abnormal cells (called dysplasia).
Through routine screenings, most polyps can be found and removed before they turn into cancer. Screening tests include visual tests (colonoscopy) and at-home stool tests (fecal immunochemical test).
Most colon cancer develops from polyps with abnormal cells that start growing uncontrollably. There are several risk factors that increase a person's chance of developing colon cancer, such as leading a sedentary lifestyle, smoking, heavy alcohol intake, having a family history of colon cancer, or having an inflammatory bowel disease (IBD).
The most important step is to talk to your doctor about colon cancer screenings. Those considered average risk are encouraged to begin screenings at age 45.1 Lifestyle factors that may also be helpful include moderating your meat consumption, eating more produce and fiber, getting moderate to vigorous exercise, avoiding smoking, and limiting alcohol consumption.
Symptoms may not occur initially, but as the disease progresses, a person may notice a change in their bowel habits (persistent diarrhea or constipation) or dark or bright red blood in their stools. Other symptoms may include abdominal pain, cramping, weight loss, loss of appetite, or fatigue.
Also called stage zero cancer, carcinoma in situ (CIS) is the earliest stage of cancer. It means that a group of abnormal cells are in the area where they formed and have not spread to surrounding tissues.
A routine examination of the inside of the colon using a thin tube with a camera called a colonoscope that transmits images. During a colonoscopy, a biopsy or removal of a polyp may also be done. This screening test can be used to help prevent or diagnose colon cancer since most people do not have symptoms in the early stages of colon cancer.
A tumor that is malignant means it has cancerous cells and may invade locally and spread to other areas of your body. A tumor that is benign means it is noncancerous and won’t invade locally or spread at a distance. To determine if a group of cells is malignant or benign, a biopsy (sample) may be taken and analyzed.
When cancer spreads from its primary location to another location in the body. Colon cancer most often spreads to the liver, but it can also metastasize to areas such as the brain, lymph nodes, or lungs.
A growth that occurs on the inner lining of the colon or rectum. Polyps are common in people over 40 and often grow slowly over many years. A colonoscopy is a reliable way to find polyps and have them removed before they can become cancerous.
Removal of a polyp. A polypectomy may be done at the same time as a routine colonoscopy. After the removal, the polyp is typically examined under a microscope to see if it’s cancerous or if there are any signs that additional removal may be needed.
Explore interactive models that show how colon cancer can metastasize (spread) in the large intestine, and how the disease changes as it progresses.
American Cancer Society. Can colorectal cancer be prevented? Updated June 9, 2020.
National Cancer Institute. Cancer stat facts: cancer of any site.
Anderloni A, Jovani M, Hassan C, Repici A. Advances, problems, and complications of polypectomy. Clin Exp Gastroenterol. 2014;7:285-96. doi:10.2147/CEG.S43084
American Cancer Society. American cancer society guideline for colorectal cancer screening. Updated November 17, 2020.