Colorectal cancer

Pathophysiology

Colorectal cancer probably arises from colorectal polyps. Adenomatous polyps convert to cancers at a rate of about 1% per year.

Treatment

Medications

Cetuximab

Cetuximab, an I_gG1 chimeric monoclonal antibody against epidermal growth factor receptor, may help according to a randomized controlled trial.

Prognosis

Staging information

Colorectal cancer staging information from the National Cancer Institute's Physician Data Query

Screening

A clinical practice guideline by the US Preventive Services Task Force has addressed colorectal cancer:

• "recommends screening for colorectal cancer using fecal occult blood testing, sigmoidoscopy, or colonoscopy in adults, beginning at age 50 years and continuing until age 75 years."

• "recommends against routine screening for colorectal cancer in adults 76 to 85 years of age. There may be considerations that support colorectal cancer screening in an individual patient."

• "recommends against screening for colorectal cancer in adults older than age 85 years"

• "the evidence is insufficient to assess the benefits and harms of computed tomographic colonography and fecal DNA testing"

A clinical practice guideline jointly written by the American Cancer Society and other groups recommends one of:

• Flexible sigmoidoscopy every 5 years
• Barium enema every 5 years
• Virtual colonography (a noninvasive test based on computed tomography) every 5 years
• Colonoscopy every 10 years

When polyps are found, a clinical practice guideline jointly written by the American Cancer Society and other groups states:

• High risk polyps are 1) 3 or more synchronous adenomas, 2) adenomas ≥1 cm in diameter, or 3) villous histology or high-grade dysplasia.
• High risk polyps should have follow-up colonoscopy in 3 years
• Low risk polyps should have repeat colonoscopy in 5 to 10 years
• If no adenomas are found, follow-up evaluation should be at 10 years

A validation of these guidelines found:

• High risk adenomas - 9% of an advanced adenoma at 4 years of follow-up.
• Low risk adenomas - 5% of an advanced adenoma at 4 years of follow-up.

Prevention

Aspirin chemoprophylaxis

A clinical practice guideline by the U.S. Preventive Services Task Force (USPSTF) recommended against taking aspirin (grade D recommendation). The Task Force acknowledged that aspirin may reduce the incidence of colorectal cancer, but "concluded that harms outweigh the benefits of aspirin and NSAID use for the prevention of colorectal cancer". A subsequent meta-analysis concluded "300 mg or more of aspirin a day for about 5 years is effective in primary prevention of colorectal cancer in randomised controlled trials, with a latency of about 10 years". However, long-term doses over 81 mg per day may increase bleeding events.

Calcium

A meta-analysis by the Cochrane Collaboration of randomized controlled trials published through 2002 concluded "Although the evidence from two RCTs suggests that calcium supplementation might contribute to a moderate degree to the prevention of colorectal adenomatous polyps, this does not constitute sufficient evidence to recommend the general use of calcium supplements to prevent colorectal cancer.". Subsequently, one randomized controlled trial by the Women's Health Initiative (WHI) reported negative results. A second randomized controlled trial reported reduction in all cancers, but had insufficient colorectal cancers for analysis.