Colon Cancer (Colorectal Cancer)

  • Medical Author:
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

  • Medical Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

Quick GuideColon Cancer: Symptoms, Signs, Screening, Stages

Colon Cancer: Symptoms, Signs, Screening, Stages

Where is the colon located?

Most of the large intestine rests inside a cavity in the abdomen called the peritoneal cavity. Parts of the colon are able to move quite freely within the peritoneal cavity as the undigested food is passing through it. As the colon heads towards the rectum, it becomes fixed to the tissues behind the peritoneal cavity, an area called the retroperitoneum. The end portion of the large intestine, the part that resides in the retroperitoneum, is the rectum. Unlike much of the rest of the colon, the rectum is fixed in place by the tissues that surround it. Because of its location, treatment for rectal cancer often is different than treatment for cancer of the rest of the colon.

Picture of colon cross section.
Picture of colon cross section.
Picture of colon cancer formation.
Picture of colon cancer formation.

How long is the human colon?

The human large intestine (colon) is about 6 feet long.

What is colorectal cancer?

Cancers of the colon and rectum (colorectal cancer) start when the process of the normal replacement of colon lining cells goes awry. Mistakes in cell division occur frequently. For reasons that are poorly understood, sometimes mistakes occur that escape our editing systems. When this occurs, these cells begin to divide independently of the normal checks and balances that control growth. As these abnormal cells grow and divide, they can lead to growths within the colon called polyps. Polyps vary in type, but many are precancerous tumors that grow slowly over the course of years and do not spread. As polyps grow, additional genetic mutations further destabilize the cells. When these precancerous tumors change direction (growing into the wall of the tube rather than into the space in the middle of it) and invade other layers of the large intestine (such as the submucosa or muscular layer), the precancerous polyp has become cancerous. In most cases this process is slow, taking at least eight to 10 years to develop from those early aberrant cells to a frank cancer.

Once a colorectal cancer forms, it begins to grow in two ways. First, the cancer can grow locally and extend through the wall of the intestine and invade adjacent structures, making the mass (called the primary tumor) more of a problem and harder to remove. Local extension can cause additional symptoms such as pain or fullness, perforation of the colon, or blockages of the colon or nearby structures. Second, as the cancer grows it begins the process of metastasis, shedding thousands of cells a day into the blood and lymphatic system that can cause cancers to form in distant locations. Colorectal cancers most commonly spread first to local lymph nodes before traveling to distant organs. Once local lymph nodes are involved, spread to the liver, the abdominal cavity, and the lung are the next most common destinations of metastatic spread.

Colorectal cancer is the third most common cause of cancer in the U.S. in both men and women. It affects almost 135,000 people annually, representing 8% of all cancers. About 4.4% of people will be diagnosed with colon or rectum cancer at some point in their lives.

Medically Reviewed by a Doctor on 4/3/2017

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