An Overview of Colorectal Cancer

Colorectal cancer is a term that refers to cancer found in the colon and/or the rectum. Cancer in the colon forms when the cells that line the colon mutate and begin growing abnormally. Most types of colon cancer begin when bulges in the intestinal wall called polyps begin to grow.

Polyps can become cancerous and spread through the colon and into organs and structures nearby. However, if a polyp is found and removed—which is easily done during a colonoscopy—it has no chance of turning cancerous.

Take a look at how polyps manifest in the colon.

Colon cancer is the third most prevalent cancer in the United States, which is why the U.S. Preventive Services Task Force (USPSTF) recommends screening for all people over the age of 50 and anyone else considered to be at high risk for developing the disease.

For people at a typical risk level, colon cancer takes a long time to develop. For those at a higher risk level, such as those who have inflammatory bowel disease (IBD), screening may need to be on a more frequent basis and should be discussed with a gastroenterologist.

Colorectal cancer can begin anywhere in the colon. The most common form is called adenocarcinoma and involves the cells that line the intestine and release fluids.


The term "colorectal cancer" and "colon cancer" can be confusing because they are often used interchangeably. This happens in the doctor's office, in articles written for patients, and in research papers written for physicians. The term "rectal cancer" is clearer—it's typically only used to refer to cancer in the rectum, which is the last part of the large intestine and connected to the anus.

Colon cancer and rectal cancer are often put together for purposes of research or in testing medications since the two types have many characteristics in common and the rectum is part of the colon.

However, when discussing a diagnosis of colon cancer or rectal cancer with a physician, it is important to have an understanding of where the cancer is located and what the stage of the cancer is. Those factors will influence treatment choices.

Anatomy of the Colon

The rectum is a part of the colon, and both organs together are called the large intestine. The colon is located around the perimeter of the abdomen and is about five feet in length. The colon is divided into several sections:

  • Ascending colon
  • Transverse colon
  • Descending colon
  • Sigmoid colon

The rectum measures six to 12 inches long and is located between the sigmoid colon and the anus. Stool is stored in the rectum until it is ready to be evacuated from the body via a bowel movement.

Further, the colon may also be talked about as having two sections: the proximal and the distal. The proximal is the first section that is attached to the small intestine (via a valve) and the distal is the second section that is attached to the rectum.

Waste travels from the proximal colon to the distal colon to the rectum and leaves the body through the anus.

People with IBD that have the condition in the colon are more susceptible to developing colon cancer. Having active IBD in the colon for a long time can increase this risk. The majority of people with IBD, however, will never develop colon cancer.

Risk Factors

There are several risk factors associated with colorectal cancer. Some can't be changed while others can be addressed with lifestyle changes. Such risk factors include:

  • Age over 50
  • Colon polyps
  • Drinking alcohol to excess
  • Family members with colon cancer
  • Having IBD (Crohn's disease and ulcerative colitis)
  • High-fat, low-fiber diet
  • Personal history of other cancers
  • Smoking or tobacco use

People with IBD should discuss their cancer risk with a gastroenterologist and work out the best screening schedule.


People with IBD will typically have regular testing, such as colonoscopy, that doubles as a colon cancer screening. This is necessary because of the increased risk.

However, there are other screening choices that might be used too, especially for routine screening in people that don't have IBD. Some of those tests include:

Colon Cancer vs. Rectal Cancer

Colorectal cancer can refer to either cancer in the colon or cancer in the rectum. There are, however, some differences between them—mainly having to do with treatment and prognosis—including:

  • Chemotherapy. In the earlier stages of colon cancer (stages 1 and 2 specifically), radiation and chemotherapy might not be given. For rectal cancer, chemotherapy can be used even for stage 1.
  • Epidemiology. This refers to how frequently diseases occur in certain people, like in men versus women. Both genders develop colon cancer about evenly, but men tend to get rectal cancer more often than women.
  • Distant Metastasis. When cancer spreads outside the organ in which it originated, it is called metastatic cancer. Rectal cancer has a higher risk of spreading to a distant organ or lymph node.
  • Local Advancement. Rectal cancer also has a high risk of local advancement, meaning that it can spread to the anus, bladder, pelvis, pelvic bones, or reproductive organs.
  • Radiation. Radiation is used less often for colon cancer and more frequently for rectal cancer. In rectal cancer stages 2 or 3, radiation might be used both before and after surgery.
  • Surgery. The most common surgery done for colon cancer is a resection. This is a procedure in which the affected part of the colon and any cancerous tissue is removed and the healthy ends of the intestine are attached back together. In rectal cancer, surgery tends to be more challenging since it's a difficult area to physically reach and remove cancer cells without affecting other organs.
  • Ostomy. Contrary to popular belief, most people with colon cancer do not need to have a permanent colostomy. After colectomy surgery, it is necessary to wear an external appliance on the abdomen to collect waste. Some people with colon cancer may have a temporary colostomy, which is later reversed, and the external appliance is no longer needed. It is more common, however, to need ostomy surgery in the case of rectal cancer. This is especially true if the anus must be removed. Without it, stool can't be held in the body (continence).

A Word From Verywell

Colorectal cancer is certainly a difficult disease to contemplate. And a diagnosis of colon or rectal cancer will require intense treatment and lifestyle changes. However, the rates of colorectal cancer are declining as more people who are at risk for it are getting screened.

Colorectal cancer can be prevented or detected early with screening, specifically with a colonoscopy. With these improvements in screening and available treatments, the cure rates of colorectal cancer are rising as are the two-year and five-year survival rates. On the horizon is the use of molecular-based stool tests, which hold the promise of making screening quicker and less invasive. The future is bright for colorectal cancer prevention, early detection, and improved treatment outcomes.


American Cancer Society. "What is Colorectal Cancer?" 20 Jan 2016.

Bartlett DL, Chu E. "Can Metastatic Colorectal Cancer Be Cured?" ONCOLOGY. 15 Mar 2012.

Ho ML, Liu J, Narra V. "Magnetic Resonance Imaging of Rectal Cancer." Clin Colon Rectal Surg. 2008 Aug;3: 178–187.

National Cancer Institute. "Colon Cancer Treatment (PDQ)–Health Professional Version." 29 Jan 2016.

National Cancer Institute. "Rectal Cancer Treatment (PDQ)–Health Professional Version." 29 Jan 2016.

More From Verywell in Colon Cancer