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Colon Cancer

What Is Colon Cancer?

The human colon, or large intestine, is a muscular, tube-shaped organ measuring about 4 feet long. It extends from the end of the small bowel to the rectum; some doctors may include the rectum as the end of the colon. The term colorectal describes this area that begins at the colon and ends at the anus. Typically, the first or right portion of the colon which is called the ascending colon moves up from the lower right portion of the abdomen. The next portion, or transverse colon, moves across from the right to the left side of the upper abdomen. Next, the third region or descending colon moves down the left side of your abdomen. Then an S shaped or sigmoid colon portion of the large intestine connects the rest of the colon to the rectum, which ends at the anus. This article will focus on the colon and less on the rectum; however, the terms colon, colorectum, and colorectal are considered interchangeable in this general article.

The colon has three main functions:

  • To digest and absorb nutrients from food
  • To concentrate fecal material by absorbing fluid (and dissolved salts, also called electrolytes) from it
  • To store and control evacuation of fecal material

The right side of your colon plays a major role in absorbing water and electrolytes, while the left side is responsible for storage and evacuation of stool.

Cancer is the transformation of normal cells. The transformed cells grow and multiply abnormally.

  • Left untreated, these cancers grow and eventually spread through the colon wall to involve the adjacent lymph nodes and organs. Ultimately, they spread (metastasized) to distant organs such as the liver, lungs, brain, and bones.
  • Cancers are dangerous because of their unbridled growth and potential for spread. They overwhelm healthy cells, tissues, and organs by taking their oxygen, nutrients, and space.
  • Most colon cancers are adenocarcinomas-tumors that develop from the glands lining the colon's inner wall.
  • These cancers, or malignant tumors, are sometimes referred to as colorectal cancer, reflecting the fact that the rectum, the end portion of the colon, can also be affected. Anatomic differences in the rectum as compared to the rest of the colon require that these areas be separately recognized by many investigators.

In the United States, one in 17 people will develop colorectal cancer.

  • According to reports from the National Cancer Institute, colorectal cancer is the third most common cancer in U.S. men.
  • Colorectal cancer is the second most common cancer in US women of Hispanic, American Indian/Alaska Native, or Asian/Pacific Islander ancestry, and the third most common cancer in white and African American women.
  • The overall incidence of colorectal cancer increased until 1985 and then began decreasing at an average rate of 5% per year in people 50 and older from 2009-2013 (available data).
  • Deaths from colorectal cancer rank third after lung and prostate cancer for men and third after lung and breast cancer for women.
  • Death statistics from colon cancer vs. rectal cancer is not clear as an estimated 40% of rectal cancers are misdiagnosed as colon cancer (another reason for lumping them together numerically).
Illustration of the colon
Illustration of the colon

Medically Reviewed by a Doctor on 10/13/2017

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Patient Comments & Reviews

The eMedicineHealth doctors ask about Colon Cancer:

Colon Cancer - Diagnosis

How was the diagnosis of your colon cancer established?

Colon Cancer - Signs and Symptoms

What signs and symptoms did you experience with your colon cancer?

Colon Cancer Causes

Colon Polyps

Colon polyps usually are benign, slow-growing tumors that arise from the epithelial cells in the large intestine. Some colon polyps contain and/or become cancerous tumors (malignant <1%). Benign colon polyps do not invade nearby tissue or spread to other parts of the body. They are commonly present in many individuals and increase in numbers with increasing age.


Read What Your Physician is Reading on Medscape

Colon Cancer, Adenocarcinoma »

Colorectal cancer is the third most common cancer in both men and women in the United States.

Read More on Medscape Reference »


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