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What Is Colorectal Cancer?

Colorectal cancer is a highly common cancer type that forms in the cells of the colon and rectum, which make up the large intestine or gastrointestinal tract, where liquid waste is converted into formed stool. Colorectal cancer is also known as colon cancer and rectal cancer; these are grouped together because of their common characteristics, symptoms and treatments. 

Colorectal cancers grow slowly, most commonly starting as growths, or polyps, on the tissue lining the colon or rectum. Some polyps can turn into cancer eventually, over time, but not all polyps become cancer. 

Over time, polyps can grow into the wall of the colon or rectum, growing outward through the layers, eventually growing into blood vessels or lymph vessels. The stage of colorectal cancer is determined by how deeply it penetrates the colon or rectum wall and if it has spread beyond the gastrointestinal tract.

According to the American Cancer Society, colorectal cancers are the third most common type of cancer in the United States. More than 149,000 people are diagnosed with colorectal cancer each year. In Colorado, there are an estimated 2,100 new cases of colorectal cancer each year.

Colorectal cancer is preventable and highly curable when diagnosed and treated early.

Why Come to CU Cancer Center for Colorectal Cancer 

CU Cancer Center doctors offer patients a comprehensive evaluation of benign and cancerous conditions of the colon, rectum and anus. As the only National Cancer Institute Designated Comprehensive Cancer Center in Colorado and only one of four in the Rocky Mountain region, we have doctors who provide top-notch, multidisciplinary, patient-centered care with improved outcomes. Our doctors are the only physicians in a 500-mile radius who are part of the National Comprehensive Cancer Network (NCCN) advisory panel. The NCCN establishes treatment guidelines that doctors all across the United States use as a reference. 

There are over 100 colorectal cancer clinical trials currently being offered by CU Cancer Center members, giving patients many different treatment options. Whenever possible, our doctors look for ways to treat colorectal and anal conditions using the least invasive techniques that can accomplish the goal.

The Colorectal Multidisciplinary Clinic brings together a team of expert surgeons, gastroenterologists, pathologists, oncologists, radiation oncologists, and more to focus on problems affecting the colon, rectum and anus. Together, the team analyzes a patient’s diagnosis and recommends a specific treatment plan for the individual by the end of the visit. 

At the CU Cancer Center, we have a dedicated treatment and research program for young adults with colorectal cancer. This program is important because young patients with colorectal cancer have unique issues, related to their cancer diagnosis and the impact of their cancer treatment.

According to the American Cancer Society, 12% of patients diagnosed with colorectal cancer have a young onset (before age 50). Over 3,600 men and women younger than 50 die each year from colorectal cancer. 

→ Recommended Colorectal Cancer Screening Age Lowered to 45 for People at Average Risk

Typically, routine screenings for colon and rectal cancer do not begin until age 45, which means key symptoms often go unrecognized. This could be one reason that young onset colorectal cancer incidence and mortality rates are increasing, even as they decline for older adults.


Our clinical partnership with UCHealth has produced survival rates higher than the state average for all stages of colon and rectum cancer

Colon Cancer Graph

Number of Patients Diagnosed – UCHealth 809 – State of Colorado 4,626
Number of Patients Surviving – UCHealth 464 – State of Colorado 2,480
*n<30, 5 Year Survival – (Date of diagnosis 1/1/2010–12/31/2014)

Rectum Cancer Graph

Number of Patients Diagnosed – UCHealth 422 – State of Colorado 2,059
Number of Patients Surviving – UCHealth 257 – State of Colorado 1,205
*n<30, 5 Year Survival – (Date of diagnosis 1/1/2010–12/31/2014)

Types of Colorectal Cancer

There are three different types of polyps that can form in the colon and rectum: adenomatous polyps (adenomas), hyperplastic polyps and inflammatory polyps, and sessile serrated polyps (SSP) and traditional serrated adenomas (TSA). 

Adenomatous polyps (adenomas) are polyps that sometimes turn into cancer, which classifies them as a pre-cancerous condition. There are three types of adenomas: tubular, villous and tubulovillous.

Hyperplastic polyps and inflammatory polyps are the most common polyps and are generally not pre-cancerous. 

Sessile serrated polyps (SSP) and traditional serrated adenomas (TSA) are often treated like adenomas because they have a higher risk of forming colorectal cancer.

Most colorectal cancers are adenocarcinomas that begin as adenomas. These cancers start in the cells that make mucus to lubricate the inside of the colon and rectum. 

Other types of rare tumors that start in the colon and rectum include carcinoid tumors, gastrointestinal stromal tumors (GISTs), lymphomas and sarcomas.

Carcinoid tumors form from cells in the lining of the intestine.

Gastrointestinal stromal tumors (GISTs) start in cells called the interstitial cells of Cajal in the wall of the colon.

Lymphomas most commonly start in the lymph nodes but can also start in the colon, rectum or other organs.

Sarcomas can form in the blood vessels, muscle or connective tissues on the wall of the colon and rectum.

Causes of Colorectal Cancer

Colorectal cancer is caused by DNA changes or mutations that occur within healthy cells. Normal cells in the body go through a life cycle where they grow and divide to form new cells and then die when the body no longer needs them. Cells contain DNA that tells the cell what to do. When a cell’s DNA is damaged, cells continue to grow and divide where they aren’t needed by the body. This buildup of cells becomes a tumor. 

Risk Factors for Colorectal Cancer

There are several factors that might increase the chance of developing colorectal cancer. These risk factors include: 

Age: Colorectal cancer can be diagnosed at any age, but the majority of people are diagnosed after age 50. Though much more common in the older populations, there has been a steady increase in cases among people younger than 50.

Weight: For men and women who are overweight or obese, the risk of developing and dying from colorectal cancer is greater. 

Race: Of all racial groups in the United States, African Americans have the highest colorectal cancer incidence and mortality rates.

Inherited mutations: About 5% of people develop colorectal cancer from inherited gene mutations. Familial adenomatous polyposis (FAP) and Lynch syndrome (hereditary non-polyposis colorectal cancer) are the most common inherited syndromes linked to colorectal cancer. 

Family History: People with a first-degree family history of colorectal cancer are more likely to develop the disease. The risk is increased if more than one relative has been diagnosed with colorectal cancer. Individuals with a family history of adenomatous polyps or colorectal cancer should consider starting screening at the age of 45. 

Personal history: Chronic inflammatory bowel diseases (IBD), including ulcerative colitis and Crohn’s disease, can increase the risk of developing colorectal cancer. Over time, due to regular inflammation and irritation, people with IBD often develop dysplasia, a term that refers to abnormal development of cells in the lining of the colon and rectum.  

Smoking: Though smoking is a well-known cause of lung cancer, it is linked to other cancers as well, including colorectal cancer. Long time smokers are more likely to develop and die from colorectal cancer.

Alcohol: Moderate to heavy alcohol use has been associated with the risk of developing colorectal cancer.

Colorectal Cancer Prevention

The best way to prevent colorectal cancer is to start screening for it at the age recommended by a physician. In 2020, the U.S. Preventive Services Task Force readjusted its recommendation for colorectal screening age 45 instead of 50 to combat increasing rates of early-onset colorectal cancer.  

There are two main groups of tests for colorectal cancer screening:

Stool-based tests: Tests that check the stool for signs of cancer. These tests are less invasive but need to be done more often.

Visual exams: Tests that look at the structure of the colon and rectum for abnormal areas.

Latest in Colorectal Cancer from the CU Cancer Center

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Information reviewed by Christopher Lieu, MD, in February 2022.