Colorectal cancer (colon and rectal cancer) is one of the most common cancers in adults. Most colorectal cancers develop slowly from precancerous growths called polyps. Screening can detect and remove these polyps before they become cancerous and can also detect colorectal cancer at an earlier, more treatable stage.

Who Should Be Screened?
 

Average-risk adults should generally begin colorectal cancer screening at age 45.

Routine screening is generally recommended through age 75.

For adults ages 76–85, the decision to continue screening is individualized based on many factors. Screening is generally discontinued after age 85. Some people need to begin screening before age 45 or undergo more frequent colonoscopy because of increased risk.

Risk Factors
 

• Increasing age — risk rises substantially after age 50, although colorectal cancer also occurs in younger adults.

• Personal history of colorectal cancer or adenomatous/advanced polyps.

• Family history — especially colorectal cancer or advanced polyps in a first-degree relative, particularly when diagnosed at a younger age or when multiple relatives are affected.

• Inherited cancer syndromes — particularly Lynch syndrome and familial adenomatous polyposis (FAP).

• Inflammatory bowel disease — longstanding ulcerative colitis or Crohn disease involving the colon; risk increases with duration, extent, and severity of inflammation.

• Obesity.

• Physical inactivity.

• Smoking.

• Heavy alcohol consumption.

• Diet high in processed meat and red meat, particularly with low intake of fiber-rich foods.

• Type 2 diabetes is associated with a modestly increased risk.

• Prior abdominal or pelvic radiation can increase long-term colorectal cancer risk.

Screenings

Colonoscopy
 

Colonoscopy examines the entire colon using a flexible camera and is generally repeated every 10 years for average-risk adults when the examination is normal and bowel preparation is adequate.

Advantages include:

• Examines the entire colon

• Can identify cancer

• Can detect and remove precancerous polyps during the same procedure

• Allows abnormal tissue to be biopsied

Disadvantages include:

• Requires bowel preparation

• Usually involves sedation

• Requires more time than stool testing

• Carries small risks of bleeding, perforation, and complications from sedation

The screening interval becomes shorter when certain polyps are found.

Stool DNA-FIT

Tests such as Cologuard look for abnormal DNA associated with colorectal cancer and blood in the stool. For average-risk screening, stool DNA-FIT is generally performed every 1–3 years, depending on the guideline and test strategy. A positive result requires a diagnostic colonoscopy.

Stool DNA testing is generally intended for average-risk screening and is not a replacement for colonoscopy in people who already require colonoscopy because of certain high-risk conditions.

Blood Tests

Blood tests are available for colorectal cancer screening in certain average-risk adults age 45 and older. The test looks for cancer-associated DNA signals circulating in the blood. It does not require stool collection or bowel preparation. However, blood-based screening is less effective at detecting precancerous polyps than colonoscopy and some stool-based strategies, so it is less useful for actually preventing colorectal cancer. A positive blood test requires a diagnostic colonoscopy. 
 

What Are Colon Polyps?
 

Polyps are growths arising from the inner lining of the colon. Most polyps are benign, but certain types can gradually develop into colorectal cancer.

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Adenomas are precancerous polyps. Most never become cancer, but colorectal cancers commonly develop through the adenoma-to-cancer pathway.

Risk is greater with certain features, including:

• Larger size

• Multiple adenomas

• Villous features

• High-grade dysplasia

Serrated Polyps- Some sessile serrated lesions and traditional serrated adenomas can also be precancerous and contribute to colorectal cancer development.

Hyperplastic Polyps- Small hyperplastic polyps, particularly in the rectum and sigmoid colon, are generally considered very low risk.

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Symptoms Require Evaluation — Not Routine Screening
 

Screening is intended for people without symptoms. A person with concerning gastrointestinal symptoms may require diagnostic testing regardless of age or whether routine colorectal cancer screening is due. Possible warning signs include:
 

• Blood in the stool

• Black or tarry stool

• Persistent change in bowel habits

• Unexplained iron-deficiency anemia

• Persistent abdominal pain

• Unexplained weight loss

• Persistent narrowing or change in stool pattern

• A rectal or abdominal mass